I can tell you from experience that this is not a good combination. The thing with B&W and Mac is there are tons of dealers that sell both, therefore it's assumed they are a good combination. And in the dealer rooms, they usually do sound quite special with a specially curated CD the dealer has on hand. The problem is when you get it home and put on real music with verve and drive you find out that the mac amps are a bit slow, not truly dynamic, and lack transparency of the top tier guys (at least when paired with B&W). Soundstage will also be below average.
The 803 diamonds need a very neutral, transparent, analog sounding amp with with loads of speed, power, grip, and extension. I had an MC205 bi-amped to them. I was speaking with a guy at audio classics at the time who said he went through the same thing, and eventually tried to put over 1000 watts of mac power in them and couldn't get what he wanted, and settled on the MC275 as the best mac choice with B&W.
I like mac amps, but they're lush so probably need to pair with some very open speakers...maybe monitor audio platinum or something.