Bryston 3BSST2 vs 3B3

I'm looking at some used amps and I would really appreciate some help distinguishing the SST2 and the cubed series. (So 4BSST2 vs 4B3 ... OR 3BSST2 vs 3B3, etc.) I've owned Bryston amps in the past so I'm not new to them. I've read that the newer cubed series has a different sound. Can anyone help? 

I know there are other wonderful amps and that recommendations might depend on the speakers, cables, etc. As much as possible, I'm trying to isolate the question to the differences between those two amps.

Thank you!