The AHB2 is a very well built amp and its got a nice heft to it despite its small size, which is plus when moving it around in the rack. Fit and finish is first class - no complaints there. Since it was a new unit I gave it some 50 hours of burn in before critical listening
I drove it first with my CAT SL-1 preamp (AHB2 set on mid gain sounded bland so ran it on high gain). It is indeed a QUIET amp - with the pre on mute, not a sound with my ears to the speakers (bookshelf Green Mountain Audio). To me the sound was very clean - almost too clean. Abundant micro details and a black background though a little lean overall. Overall it sound a little sterile for my taste - something like what you might expect to hear in a recording studio monitor I assume (I was reminded a little of my listening session with Genelec studio monitors which had a similar sound signature). Pace and rhythm was very good, mids were very clean but the overall presentation lacked something (the emotion?) which to my mind is that critical glue that binds all the elements of the recording and presents it as music.
Next up I drove it directly from the analog outputs of the DAC2 (DAC2 set to 0dB and AHB2 to low gain as is recommended). This combination felt like a better match (even quieter and with more perceived drive) but the sonic signature didn't change much - and it was still a little lean and that sterility factor persisted - perhaps even more so.
I appreciate all the technology that has gone into making the AHB2 and the small form factor, great finish and substantial 190W @4ohms from a small chassis, But I wan't swayed enough by the sound to pull the trigger to purchase it. Also, my own sense is that while the amp has three gain options to make it a suitable match for different pre/DACs etc, it was probably mostly conceived as a partner for the DAC2.
YMMV