Hi!
I used the Cantate 2 together with AKG's K530, K701 and Sennheiser HD650. My other amp is a Vincent KHV-1... so much about my experience, or lack thereof.
Describing the sound of the K701/Cantate pairing on it's own, there's something missing to me: Too recessed mids, too little bass and far too harsh treble when using the chinch inputs. Via USB, the cantate gets a little better bass response, and bit rolled off highs (though still very bright)
Overall, I like the Cantate's USB mode a lot better than its sound via chinch (which may as well have to do with my source - an Audiotrak Prodigy 7.1 HiFi soundcard, with swapped OPA2707 opamps)
In both modes, the Cantate/K701 combo delivers a fantastic soundstage (especially with crossfeed on) that I haven't heard from any other amp/headphone combo yet.
However, there's a problem with the Cantate - at least for me: It sounds very analytical and precise ... but it just doesn't sound musical. At first, I was impressed by this kind of sound reproduction, but a few weeks later, I just could stand to hear it any more: though the soundstage is wide, almost any instrument is played at the same volume, so that makes the soundstage very flat in turn. Combined with the overall bright signature, it just wasnt the right thing for me.
The AKG's enhance on the Cantate's traits quite pronounced, so if you are into the analytical thing, this may be a very good combo. If you just want to enjoy music, there are better setups out there.
In my case, this was a Vincent KHV-1 with AKG 701's or Sennheiser HD650's. The KHV-1 is a darker sounding (hybrid) amp with tons of power (you get a feeling, that the Cantate has a lack thereof) and a quite aggressive (or rather engaging), but under no circumstances fatiguing signature. It just brings music to life for me, though it's far from analytical and doesn't produce the same impressive soundstage as the Cantate. However, the Vincent's soundstage has immense depth, achieved by playing seemingly every voice of a track at a different volumne, with the quietest ones still clearly hearable.
