In a world you don’t get some real time with TrueBass, you don’t know what you’re missing, and if you don’t use it for a while you can forget how great it is, but listening to some electronic music through my Hemps (think RUFUS DU SOL or Elderbrook), and it’s just another level. Amp is a G111 for what that’s worth. I like the ability on my Zen to both stagger the gain with a button, and a knob, and the TrueBass, and for the knob alone I might never leave the Zen, but going for a TOTL Signature has crossed my mind. I’m not sure if the performance would be worth the money, considering you’re paying for the amp part as well, and the volume control isn’t as good, but I do know that owning iFi DACs if only for that TrueBass is something I can live with regardless of my finances. I’d love to A/B my G111 against something like the signature to see if I could move to one unit, and then just give up my 880s. Got off on a tangent there- really just came to gush about TrueBass and how it makes me totally content with never leaving the iFi lineup. If iFi could now please just come out with a Zen that’s DAC is as quality as it’s best stuff AND has true bass I’d be the happiest boy on earth
Though it isn’t as much of a bass boost as the ifi, bursons v6 vivid dual opamps are such a richly textured and amazingly well done tonal change to anything you can cram them into that I could do without ifi bass if i had them in whatever amp or preamp I’m plugged into. They can even go into a lot of dacs in their preamp stage. Worth every cent.
music is about much more than bass. that is one of the ingredients but far from being even one of the important ones. that said, I’ve never turned off the TrueBass on my iFi Zen since I got it. 
Yeah totally depends on the headphones and music. I never use it with the 880s. I can tell you the enjoyment I get out of my music is way higher using the bass boost on the iFi then it was going from a Zen to the Denafrips Ares II (Which I ended up selling)
I have an ifi xcan and love the bass boost. It was my 1st amp/dac. Pretty much ran the boost all the time until I over did it with a pair of Cascades (without filters) listening to jungle at a high level. Was good at the time but messed with my ears making them sensetive to bass for a few days after. Recently I was lucky enough to get a Burson C3R with the vivid opamps and totally love it! The ifi has a little bit more bass and slam but the Burson is WAY more detailed and textured as well as being wider and cleaner. I use my clear pros and sony z1rs solely on the Burson now for everything. But when I feel that need for full on bass its back to the ifi with the bass boost on and my LCD-2closed. Theres just something about ifi bass boost and planar sub bass that can’t be beat! If I could only have one unit it would be the Burson but for jungle, dnb, trip hop and electronic music I have to go the ifi.