Hello,
This one was somewhat an impulse purchase - as I am a completionnist and really, really curious about this one. In fact, this not really that a usless purchase as my new DAP (FiiO M11 Plus) is not that powerful plus I live somewhat in two places, so I did not return this even if maybe I should have...
First remark : my unit is not noisy at all and I have either been really lucky with my Cayin gear, or problems are rare, or even my very slight tinnitus covers it (I doubt it as I am pretty sensitive to noise but who knows ?). I only used it unbalanced with all combinations of settings and outputs (low and high impedance) and all is OK.
I am pretty happy with the power of this thing, it seems to drive my AKG 712 Pro really fine, surely better that the FiiO alone or than the (closer-sounding) motherboard. I do not know how to descirbe it but there seems to be more resolution and a cleaner signal overall (with better separation also), this is particularly clear on the AKG. Actually, I did not really liked the K712 but with this I actually like what I hear, I do not know why since it goes against my beliefs but the overall difference makes it sound "full" where I found it a bit lacking.
The combination with the iDac-6 Mk2 is quite an interesting pair since I can chose tube sound (which is really better for the Sennheiser 560S but not that greath with the AKG) or SS sound (which is better for AKG 712 Pro). Of course, a real tube amp like HA-1A Mk2 produces a more refined sound, but overall we got a similar experience with the benefit of a very versatile and powerful gear with the i-series stack.
If I can confirm that there is no noise with the balanced setting, that seems to be a pretty solid endgame candidate : plenty of power, no colour added to the sound, very solid performance, not that expensive (for Hifi gear), very good form factor, good-looking.