Hi registered here just to type a short review.
I'm a long time iFi Zen DAC user, first Zen DAC was a simple and one of the most budget solutions to control both cans and active speakers - that's why I bough it and immediately loved it's "analogue" sound. ASIO, drivers, firmware etc - all good all working fine. Just as it should be. Later, after selling all that stuff, moving to another country, switching to laptop etc I decided to get some Zen again and this time it was Zen Air DAC (got it for ~90 euro I think) - hard to say without direct comparison but it seems to sound at least as good if not better (somewhat cleaner? more refined? not sure). I didn't need bal connection, SE only, so it was overall the same for me until I got Senn 6xx cans. Well, there's no distortion at all even at max volume and it's louder than I need but not crazy powerful it feels so I decided to make a bit of upgrade - add both more power to cans (and maybe a bit cleaner output) as well as try to connect my current Adam T5Vs with XLRs with that nice 4.4-to-XLR cable(s) iFi makes. I was also glad to see USB-C because - for my laptop at least - it means few times higher current output (I think is 2-3A instead of 0.5A) and overal should be better just "electrically".
220 euro is not a big deal anyway so here is it, Zen DAC 3 with it gorgeous look, finish and feel. I played some tracks on Air and then switched to Zen 3. Well, that was one amazing change - more dynamic, airy, more resolving sound with better and fuller bass and way better (but definitely more present) treble. Wider sounstage exceeding speakers and so on. Overall "tune" seems to be the same but on a new relosution level and not as calm and laid back. Swithcing back and forth between Air and Zen 3 confirmed that.
But something made me do an experiment: what if I connect Zen 3 to the same USB-A port using iFi "kit' cable.
There was a big change again. It changed back. The "old" Air sound returned in all its "analogueness".
Well well. Now I'm waiting for ordered USB-C to USB-B cable to check what's Air capable of. Balanced cables are on the way as well and I'm not going to return Zen 3, I like it appearance.
I don't believe that what I've heard is "USB cables sound different". I hear no difference between "kit" and longer cable I got for Air. Amperes matter more and there's a huge difference between A nad C ports - on my laptop at least.
What else? Power Match now doesn't make pop sound on switching on and off.
It still affects both HP and Line out (I need it Variable due to speakers).
There still is sort of difference/richer and fuller sound - in speakers! - with PM on and more sterile sound when it's off, maybe less compared to Air.
HP out still works no matter if you plug headphones in or not and that's what iFi needs to change (not only my opinion). The good thing is, unlike Zen DAC 1 both Air and Zen 3 have no sounds in line out when you (un)plug your cans. Honestly I'd prefer to have any hardware switch to select line or HP out (or both).
The biggest issue is a classics again: laptop loses Zen 3 same as Air on waking up after sleep. And you need to manually switch the cable off and on. That's not my exclusive experience as well
P.S. Tried GTO firmware on Zen DAC 1 and after a hour of exciting "whoa just listen to all the details" realized that to my ears it's rather distorted, artificially sharpened fatiguing sound.