I've been reading the discussions and, "wow"... Pretty polarized opinions. I will stay away from the commentary regarding pricing/value, and age of chipsets. All that matters to me is "sound quality", so that is what I'll stick to:
So in full transparency, I was selected to TRY the ZEN CAN SIGNATURE 6XX AMP because I've bought and offered feedback on multiple iFi products in the past. I've only had the unit since Friday 7/17, (It's now evening 7/20) so I can only offer my INITIAL impressions and ideas of benefit(s). Does the amp have plenty of power? Yes. Is the amp quiet enough for iems? Yes (With my Thieaudio Legacy 3 iems both 0db and 6db are dead silent for "noise", and I feel that the 0db setting was plenty powerful enough for them, with 6db maxing-out my loudest listening threshold by 12 o'clock on the volume.) With my original 6 year old HD650, the straight performance was comparable to my THX SP200 or iFi iDSD Black Label, (Single-Ended only) and superior to my Cavalli LCX +SDAC with no iFi "enhancements" enabled. However, when I turned on the "HD6xx" and "X Space" features the HD650 felt "corrected". Yes, my iDSD has "X-boost", and "3D" enhancements as well, but they don't sound purpose-built to my HD-650 like the Zen CAN's enhancements sound to me. The soundstage spreads "dynamically" appropriate to what is being played, which I can't reproduce manually with a single EQ on any other amp. (That's including my Schiit Audio Asgard II, iFi xCAN, or iCAN Micro as well.) The bass gains a bit more authority, yet is crisp with sharp attacks, and not bloated or smeared sounding on the decay. The treble extends and opens without becoming harsh, sibilant, or "shouty", and the midrange feels a bit less recessed and "fuller" without feeling busy or compressed. How I wish the HD650 sounded from the start without going to the extremes of the HD600. (Which still would lack the bass I'm hearing.) I hear no HD650 "veil" at all. So do I have other amps that power my HD650 well? Yes. Do some cost more while other cost less? Yes. Do ANY of the others "fix" my HD650 sound signature to be more to my liking with the touch of a button? No. Does this amp increase the versatility of my HD650s for more types of listening to music? Definitely. My HD650s are more "all-rounders" with the Zen CAN Signature. Before I only used them for jazz and mostly female club singers because their "quirks" lent themselves towards that type of atmosphere and vocal range. For Analytical; Beyer T1(ver2), for Rock; ThieAudio Phantoms, for "general listening"; HiFiMan Sundara, for JPOP/EDM; Modhouse Argon. Nice thing is that the Zen CAN Signature drives all of these equally-well too. (Especially using the "HD 6xx" and "X Space" effects with my ThieAudio Phantom!)
Just thought it would add value to hear someone speak about their actual experience regarding performance of this device with their personal headphones. Hope this helps someone.