For sound of the 4B-SST²I would say it is neutral. It gives you what you put into it back out, just louder.
With the word neutral I do not mean thin sounding, (which is what some folks assume neutral means.) The amp has a good balance of highs mid and bass. Musical sounding. But no bloated mids at all.
My last amp, a Forte 4A was great. I had to have a better sounding amp to fork out the money.. And after auditioningthe Bryston 4B-SST² i felt it was better. The best part is as I have made some other improvements to my system the Bryston 4B-SST² has easily kept up. And I am certain it can do even better as I refine my setup.
So I would say I love my Bryston 4B-SST² and it is all i need for an amp for the forseeable future.
I am not some Bryston sop.. I tried the Bryston DAC and returned it as my cheap DAC ($250 used ten years old) was just as good IMO. So with that clearly I am not 'just' a Bryston fangirl, I reiterate the 4B_SST² amp is a real keeper.