Here is my amateur (and somewhat long, sorry) review of the Hip-Dac…
TL; DR → The Hip-Dac is likely the top dog in this product category at this price point – IF you fall into a somewhat narrow range of use cases. iFi has addressed some ergonomic issues that plague this product category, but not some others. The presence of the balanced output is both a big pro and a somewhat smaller and potentially confusing con. The Hip-Dac sounds quite good with a warm sound signature. It sounds really good when it’s driving a balanced headphone/iem that has a brighter signature but can sound too dark if it’s driving neutral-to-darker ones.
I write this with several hours of listening to the Hip-Dac from both the unbalanced and balanced outputs. For additional context, the Hip-Dac is the 3rd of these flask-styled portable DAC/amps I’ve owned and have significant experience with. The first two were the Fiio E18 and the Topping NX4-DSD. Why am I on my 3rd such device outside of just being an audiophile nerd? The E18 developed software issues inside a year causing my Windows 10 laptop and my Android phone both to freak out in weird ways. The Topping’s micro-USB connection is FRAGILE and quickly loosened to the point where connection was regularly dropping from my phone. So on with the Hip-Dac details already…
Ergonomics & Build:
I can’t really add much that @epic225, @ZeosPantera, and others have already said in terms of positives, but have comments on the issues the Hip-DAC has not solved. The Hip-DAC a well built, robust feeling device, and the color is fun without being too flashy. The recessed male type A USB connector is a big positive feature, though. The recess cutout is large enough to accomodate a wide range of female USB type A jacks, too. I have yet to find a USB extension that doesn’t fit. They probably do exist, but I haven’t found one yet. I have been able to plug it into my phone, plug in headphones, stick the phone & dac in my coat pocket, and go for long walks without jostling a cable to the point that the connection drops (the dog was also a huge fan of this phase of testing). That was a big problem with my NX4. iFi seems to have licked that particular problem. However, it’s still not a pocket friendly solution:
(Crappy photo quality due to having to use my Kindle Fire tablet to take the picture. Please don’t ask why I didn’t just use my phone for the photo 
) There are wires sticking out both ends of the Hip-Dac. That USB OTG cable pictured is not the stock wire and is LESS stiff than the stock wire, yet still holds up one end of the phone all by itself. A 90 degree balanced adapter would help some, but that’s a lot to slide in and out of a pocket. It works in the pocket of my winter coat, but in the summer can I put that in the hip pocket of my jeans and walk around without carrying it in hand? Doubtful. But this is not an issue specific to the Hip-Dac. This is an ergonomic problem this product category has yet to figure out as general rule, it seems. On one particular walk the snow was melting and there was mud and puddles everywhere. The dog got filthy. I had to text home to have them get a towel ready to wipe her down before she got mud everywhere. Fumbling the phone, Hip-Dac, wires, and trying to text while holding onto one end of a leash was a challenge. So an area for improvement in this product category – at least until true wireless tech reaches truly equal quality levels – is to figure out how to make these devices more actual OTG-mobile friendly. Thus, this is not a specific complaint about the Hip-DAC, more just a comment on one ergonomic area the Hip-DAC has not solved. Or do I just deeply misunderstand the use case of these devices? If I do, please tell me and explain why.
One potential appeal of the Hip-DAC is MQA. I did not test this because I’m no longer a Tidal user. Also, in response to the iFi Zen DAC thread on this forum and issues that showed up with its slow switching between different sample rates, I had no issues with that when playing through a Windows 10 laptop.
Sound:
The Hip-Dac definitely has a warmer tilt to the sound, likely due to the Burr Brown implementation. The amp may also tilt warmer, but there’s no way to test the amp and the dac separately (no line out or line in). It’s signature is the warmest out the three portable amp/DACs with which I have significant experience. I tried Ikko OH-10, Tin T3, HiFiMan/Massdrop HE-4XX, Senn/Massdrop HD-6XX, and Beyerdynamic DT 880 600 ohm. The warm signature complements brighter cans/IEMs really well. The OH-10 (pronounced V signature), HE-4XX (less V than OH-10 with slight W signature), and DT-880 (neutral-bright signature) can all sound sibilant when driven with an analytical amp (think Atom or THX here). To my ear, sibilance was only ever an issue through the Hip-DAC when the recording itself was really sharp. For example, Alanis Morissette’s You Oughta Know just IS sibilant. The Hip-Dac makes that less objectionable, but doesn’t remove it. Otherwise, many of my other sibilance tests came up roses. However, there is less “air” to the sound here than even other portable DAC/AMPs. The NX4 has lots of power, but is also treble ear-murder at times, as an example. This lack of air became problematic on the HD-6XX. The 6XX is reknowned for it’s neutral-warm signature and it just sounds dark, veiled, and lifeless on the Hip-Dac. When Hip-Dac was paired with brighter cans, I didn’t notice poor imaging or soundstage, but nor were either of those things reference caliber. Vocals sound pretty good as well. If anything they can at times just edge up to the line of shouty/honky, but only rarely and with certain vocalists. I should also disclose that I’m upper-mid sensitive and thus perceive shouty/honky faster than most. This aspect of the sound may not be an issue for most listeners.
The balanced performance does improve things like imaging and soundstage and noticeably increases the power. I don’t think I’d call it a “night and day” improvement, but it is noticeable. The overall warm sound signature remains too. I was hoping the balanced output would perk up the treble on the 6XX, it did not. However, using balanced out on my 4XX and going for a long walk was pure joy (at least from a listening perspective). The sound I got just walking around was wonderful, and definitely the best mobile sound I’ve been able to cobble together yet within my budget. I will be doing that as often as I can. Overall, however, the balanced output adds detail and improves separation. By comparison, the unbalanced output takes on a veiled character.
I agree with previous reviewers that the XBASS boost is well done. It does a great job of introducing more sub-bass and adding slam without bleeding into the vocals. Deep male vocals don’t take on a chesty character. And it’s here where the power of the Hip-Dac shows up. Even with the XBASS enabled, the bass is always tight and controlled. The unit just SOUNDS powerful and under control - even if it may ultimately not measure to the same output level of the NX4 (it might though, I just don’t know). The XBASS can be too much with different songs and different headphones. But it is overall one of the better bass boosts I’ve heard.
One other gripe:
I do somewhat question the inclusion of the balanced out on a $150 portable DAC/AMP. A balanced cable for a HE-4XX costs about $60 on Amazon right now ($45 if you go New Fantasia - which, don’t) and that’s pretty close to going rate for balanced cables. Luckily I already had one, but had to get a $22 adapter to use it with the Hip-Dac. At those cable prices, using the Hip-Dac balanced doesn’t feel like I’m using a “budget” product anymore. I definitely appreciate the extra power output and cleaner sound, but I’m torn on whether iFi should have gone with the balanced or scrapped that and put the additional money into maximizing the performance of the SE output and included a line-out.
Bottom line:
IF you already have balanced capability for or are willing to spend money to get balanced-capable headphones/IEMs with bright-ish treble response and are looking for a relatively inexpensive OTG option, the iFi Hip-Dac is a homerun. If you need a mobile solution and want to start exploring the world of balanced over time, the Hip-Dac is also a solid option to build around. If you’re interested in the Hip-Dac just to have a budget entry into checking out MQA, I recommend caution. Synergy between amp and headphones is very important here, and the unbalanced performance is not spectacular. Yes, it’s a true statement that synergy is important everywhere, but there is a world of difference in the sound here if the Hip-Dac is paired with darker headphones vs. brighter ones. However, if you’re very treble-sensitive, the Hip-Dac may be right for you even with darker than average headphones.
OK, I’ve said quite enough already. I hope someone out there finds these thoughts useful. Enjoy the music everyone!