Without the luxury of trying both in your system, I think either amplifier will drive your MA RS6 speakers quite satisfactorily. The NAD has greater headroom but might sound a bit dry compared to the Cambridge. BTW, Chip Stern reviewed the NAD C370 quite a while back (2002) and found it a true blue collar champion of a honest day's work for a honest day's wages! Although I have not heard the NAD C370, I am always impressed with how NAD can pack so much for so little money. I remember hearing my friend's NAD 3040 (I think, anyhow, its a classic now) and came away very impressed with it. I have heard the Cambridge gear before, and yes it might sound sweeter than the NAD and is also a very good piece of gear. Your speakers are pretty easy to drive, but NAD's extra headroom might be advantage in giving you more controlled bass.
Either choice will be excellent!