I’ve bought the PC38X(for its decent price) and looked for the Schiit Hel 2 for my PC, but I’ve read reviews that the Modi+Magni is better, also I’ve seen many streamers use the GoXLR, which even has game/chat balance adjust. Then I started to think that I might never need a DAC/AMP since my motherboard is a 1000$ ROG Maximus 13 extreme. I’m quite confused about where to plug my headphones for the best sound quality. I want to have mic gain controls and game/chat balance controls. Can I get some advice for choosing my headphones’ source?
When you are looking at the GoXLR, I would strongly suggest looking at the Yamaha AG03.
Gives you a lot of options and using a TRS to 2x TS Y-Splitter (such as below), you can have voice chat from onboard and game sound via the mixers built in DAC.
Budget Range Amp fed from onboard audio would do.
Defenitly don’t plug your headset in the front panel connectors cause the unshielded cable through a PC case doesn’t make for good audio 
Try plugging it in your motherboard or an external DAC/Amp
Does the AG03 have better headphone outputs than the Goxlr mini? Also, Are there any Mixamp alternatives that have good audio quality?
I would not go with goXLR because I do not like the digital, software based design imo but that is just me. I would go with motu for any higher end audio. I have heard good things about it but I do not know anything about the true capabilities MOTU UltraLite mk5. BUT it is 622 pound sterling or about 700€ and overkill for many except if you ever want to use XLR mics and be fine for years??
Talking about ROG motherboards. I use a 3700x on a Asus ROG 570e and the sound is worse than my bad Dell XPS13 2018 and worse than the Z77 DS4 3rd Gen intel
Since I never used the GoXLR (or goXLR-mini for that matter), I can’t say.
Main downside I see from looking at the GoXLR online is the fact it is basically a front-end for software. In that case, you could also use voicemeeter and a USB-Midi Controller.
The AG03 is solid audio wise. Simple to understand layout and functions that make sense as a stand-alone desktop solution.
Mackie BigKnob Studio exists aswell, more monitor controller than mixer though.
The SSL2 is another option, same price class as the BigKnob. Less features = Higher quality features.
Usually, people run mixer and audiointerface as separate devices.
In your case with the PC38X, the AG03 will be fine. Can always add a dedicated Headphone Amp after it.