Interesting, as I heard them on the N800's and they sounded fabulous. In fact I preferred them over the MC501 McIntosh monos, which are considered by many to be the best amps for the N800s. It appears that there is some special synergy happening here. I always thought the Nautilus series sounded a little hot on top and slightly dry. The N800 are beautifully neutral, but they still have a touch of this familiar B&W signature. The CAD 500's are voiced a little on the sweet and lush side and that's probably the reason why they mated with the B&W's so synergistically. I think these amps have one of the best midranges among solid state amps. Here they really sound very tube-like: rich, liquid and with gorgeous tonality. The N800's are definitely not an easy load and the Cary's could handle them with no signs of strain or compression, always sounding open and dynamic.
To sound best they should be paired with a high gain preamp, such as Cary's own pres or any of the Suprateks, which BTW are excellent.