I owned the BP20 and also owned Bryston amps in the 1990’s. I also had a Thiel SCS4 monitor with a Bryston 7B-sst and I think a BAT VK-42SE preamp (warm).
The combo of the BP20 + Bryston 1997 + Thiel would be too bright for my ears. I would get a warm-ish Class D amp, such as a D-Sonic