New to the B&W 801D4

B&W 800 series speakers love power. Add Pass Labs X600.8 mono amps to your list. Also, I am sure the MSB preamp section is decent but if you want better layering, better soundstage and more natural sound, consider adding a good linestage in the future, solid state or tube. 

I would probably add a preamp before I changed amplifiers. That might be a better result. Those are good amps by most accounts.

@audiozink 

I auditioned the D4s powered by a Luxman D10X—glorious sound, detailed but not overly analytical. Vocals were warm and eerily lifelike. I'm unsure of your listening levels, but your room is the size of a basketball court! B&W needs power to sound their best. 

Aside from Luxman, I think McIntosh will adequately power them and provide tremendous midbass/bass. I have a pair of MC611s powering a pair of KEF Reference 1s. These little guys are a nightmarish load to drive, but the 611s can easily drive them. Within your budget, don't overlook the MC 1.25KW amp. That would be my choice without question. Looks cool too!