COot,
DEscribe your room size and any special considerations acoustically.
I have run my 5s off 120, 180 and 350 and 500 w/ch 2 channel amps in my 20X30 L shaped room with standard height drywall ceiling and carpet over concrete floor.
ALl these were "suitable" for low to moderate volume no doubt, the more power and current, the merrier, for the "biggest", fullest sound. All amps were limited in terms of biggest sound possible compared to my current 500w/ch BEl CAnto ref1000m Icepower monoblocks.
I would recommend 500 w/ch Class D or something similar for best results with the largest OHMs. Current delivery capability is as important to overall tonal balance as # watts is for distortion free higher SPLs often needed to reproduce large scale works at a realistic level in a larger room.
My smaller 100s make due nicely with "only" 180 w/ch in most any room in my modest size house I use them in, but current delivery is also critical. Your B&K might be the bottleneck to best large scale "big" performance possible. More watts and perhaps even more current as well to go along with that will surely take things to a higher level, assuming everything is in good working order.