I had a B&K 507 S2, it performed very well with B&W speakers, but when I upgraded my speakers to Totem (which I not longer have), I found the 507 to be too bright in the amplification side with these speakers. When I ran the pre outs to other amps (pass, CJ and others), this brightness greatly diminished - hence my reasoning that it was the amplifier side of the B&K. I have had a forum conversation recently with another fellow that he runs B&K M200 amps with Totem speakers and does not encounter this issue. Other than with the Totem speakers, I felt the 507 S2 performed well in HT and very good (for an HT receiver) in stereo, but certainly no comparison to a decent 2-channel preamp amp combo. Is it a step up from the Marantz and NAD, I think it depends on the models you are comparing. I liked the NAD T773 (I think this was the model), but ended up with the B&K, not so sure it was a big upgrade over the NAD though. No experience with the Marantz so I cannot comment.
