i liked the 6550 SE... it doesn't go as low and as loud as the similarly powered scott but that's how i like it late in the evening, when my speakers put out too much bass that i need to tone it down, otherwise the neighbors will petition my eviction... at moderate to slightly loud volume, the 6550 driving my ms902's can go toe-2-toe with my accuphase/ms908 in terms of sound quality... in fact sometimes i think its even beating it, and considering the price difference (20k+) i would say its slaughtering it... i'm not talking about quantity, but quality/musicality... it doesn't have the absolute bass extension of the accuphase/ms908 combo nor its capacity to go loud but it's "just right" for enjoying the kind of music (vocals/acoustic) i listen to at midnight.
and the scott... hmmm how should i describe it -- graceful & strong... bobby enriquez playing wild piano was EXPLOSIVE !! the guys were listening at 3 o'clock volume using my ms908... with built-in phono and line stage, couldn't ask for more... whatever the source & speaker, i have yet to hear the scott sound less than magnificent... the epitome of what i want in an amp, full-featured yet priced just right, and sounds wonderful.