I have just had a play with a 4B ST for the last few weeks, I was offered it at a price that is frankly obscene it was so cheap.
However, I found it quite harsh sounding, I was going to use it in the bedroom, where I have an Arcam FMJ amp, a pair of Roksan Ribbon TR5 speakers and a Rel Stentor Strata sub, so a budget bedroom system.
Hand on heart I actually preferred the sound of the Arcam on its own rather than using it as a pre.
I also had an old Parasound 6 channel amp, and I did an A-B of that and the Bryston, again the Parasound won, just sounded a lot smoother and grown up.
I was seriously disappointed, so much so that I knew I would not use it so I gave it back and let him sell it for 3x as much as he offered me for it.
I used to use the small Classé CAV-180 amp and that was divine, used it with a Meridian Processor and it just rocked. I have gone DSP with Meridian speakers now, but if I were to go back to analogue speakers Classé would be one of my first choices. Also the Parasound Monos are awesome and can be had used on budget I reckon.
BAT VK-2300 is also worth digging out, mate was using this and it is something else, he had it in 5 channel config, but as a stereo power amp he has only bettered it by the big Levinson Monos on the main channels.