I didn't audition too heavily, but another one that I did listen to was the Sunfire Cinema Grand II which is another popular amp run with the ref 50 which sounded fine at the time, but it was at a friend's place with a Ref 50 with stock power cords, single-ended connectors and everything else that was different between his and my systems. We never actually exchanged amps to compare directly.
One thing that is apparent between the two sounds that I attribute to the amp, is a slightly more relaxed/natural sound.
Like I said, there were a lot of variables that could affect the final sound, but in asking around at a couple of the shops near me that carry or have heard both products, that's been their comment too.
I haven't heard the Classe.
Hope this helps.
Russ