Cary CAD-500 MB. I realize that these are above your budget ($4,000 - $4,500 used), but they are absolutely the best match I heard with the Nautilus series. My second choice for the 802N's would be McIntoish MC501s. I would strongly prefer the Carys though. It's amazing how tube-like rich and liquid they sound. Dennis Had did a terrific job tuning them to sound like his best tube offerings combining it with all the effortless dynamics and bottom end that only monster solid state amps can deliver. These amps can put out 1,000 watts into 4 ohm with lots of healthy current. That's exactly what the B&W's need to sound their best. You should definitely try them out. Their rich and lush midrange will provide a very synergistic match with the B$W's slightly dry upper mids and treble.