Running my N802s, I recently upgraded a Pass X350 stereo amp to X600 Monos. Unbelievable Difference!!! Especially in the base and transparency.
You've got to ask yourself, however, is it a better sounding amp or is it the added power. Probably some of both, but I suspect more because of the better sounding mono amps.
Focus on amp sonic qualities, as much as power. You've got a great system now and plenty of power, but may want to experiment with changing the sound if not satisfied. If you upgrade with ML gear you may want to try the 33H as an upgrade (less power but better sonics). I don't think a ML336 is going to sound much different than the 335, since they are basically constructed the same way. Going to monos can probably help as much as anything.
Finally, contrary to ratings and many of the above postings, the B&W 800s can demand difficult loads at various times with different source material even though they are rated at 8 ohms. This is where the added power comes in handy.
Good luck & happy listening.