What Choice for Nautilus 802

Try one MC-352. If it still isn't enough juice, monoblock the first one, and buy another. MC-352s can be had for about $2,500-$2,700 and double for a monoblocked set.
Much better than the 501s, IMO.

Might want to call Frank Gow at Audio Classics in Vestal New York ... 607-766-3501 ... if you do not recognize the name, he is the son of one of the founders of McIntosh.

I have the N802's and run them with an MC-352. It's a very good combination. The Mac 402 or 602 are excellent with
N802's as well. The 802's do need plenty of power to sound
their best.

I can't speak for McIntosh, but what ever amp you decide on make sure it's at least 200 watts per channel high current. I have N802's. Started with a 155 watt per channel crown DC300A. They sounded okay. I then Bi amped them with two crowns. That made them sing at approx 300 per speakers. Couldn't leave well enough alone so I went to a PSA pushing 400 per speaker. That really brought them to life.I spoke to a B&W engineer there feelings is the more clean power you give them the better.
Happy listening