Sounds like your setup is something similar to mine. I also have B&W Nautilus 801s as main L/R speakers, but I use Matrix 801 S3s as rear surrounds, with Nautilus HTM-1 as center speaker.
I have given up on using a two-channel amp to drive two speakers. I found that bi-amping has given me the best results. It seems that the absolute power rating per channel of an amp does not affect the sound as much as dedicating two channels of amp power to each speaker. That was true even with Class A 2-channel amp on two speakers, versus bi-amping two speakers with 4-channels either from a two 2-channel amp, or from a 5-channel amp. I learned about bi-amping from my audio dealers, who highly recommended that I try it out, and now I am fully convinced of its merits.
I now use a Krell KAV-1500 (5 channels x 300watts/channel) to drive my N801s, a Meridian 557 (2 channels x 200 watts/channel) for the HTM-1 center, and a JBL Synthesis 650 (5 channels x 130 watts/channel) for the B&W Matrix 801s. All I can say is that this set up sounds pretty phenomenal. Total price of the three amps is less than $7K, with the Krell purchased new, and the other two amps purchased in mint condition on Audiogon.
As Slartibartfast mentioned above, you will get even better results if dedicated 20 amp lines are used though.
Good luck in your search!!!