If the Mark Levinson didn't offer something more, I'd be a bit worried - one of their stereo amps is likely to set you back quite a bit more than a 990/7700 combo.

My Model 750 is now two generations removed from the current Outlaw surround amps, and I'm still very happy with it. I also owned a Model 950 prior to getting the 990 and would agree with the Outlaw you talked to - the 990 is a great step up from the 950. While I can't speak to the exact match-up in question (haven't heard the 7500/7700 and have only limited experience with B&W's speakers), I do think the 7500 would be a good match with B&W's.