Hmm that's interesting. I actually do find the BL5s to be bass heavy (NOT boomy), and almost don't see how they COULDN'T be with that massive 15 inch woofer under each one. I actually have the Bass control on the Beomaster turned down to -1 to slightly compensate for the bass. But this is possibly because I come from BeoLab 1s and what I consider my reference standard, the Wilkins 802 Diamond which, the BWs particularly, have a delightful and crispy midrange and sparkly highs. Very "RIGHT THERE" presentation like being at a live performance. I would imagine them to be a great match to a BM8000 as a matter of fact, with their power hungry requirements. The BL5 is quite laid back. Someone in a BL1 review once compared the sonic signature of the BL4000 with the BL5 (not comparing the speakers directly by any means) which I would say is accurate. At one point I made the comment to Peter in the what B&O would you keep thread that for sure I'd get rid of everything else I owned just to have a pair of BL5 if I HAD to. Now after having them I don't think I would sacrifice everything else.
Raw clean power is one of the beautiful things about the BM8000 actually, that it can drive just about anything you can throw it at it with that dual-mono high power amp design. I'd agree that within the B&O range, the MS150 would be my choice almost without question. Would love to hear a pair one day.