Another vote for the Cambridge 640P. They're not even $180 unless you're talking about shipping. They're $169 pretty much anywhere, including Audio Advisor and MusicDirect.
This thing is incredible. It has a lot of the performance you don't usually get until you pay some serious money, such as a very high s/n ratio (the noise floor is LOW!), linearity, speed, and frequency extension at both ends. You will hear a significant improvement over your NAD, and may not hear much more improvement beyond the 640P until you get to a Graham Slee Era Gold Reflex at $925.
I was playing my analog rig into a vintage but highly respected Amber Model 17 preamp. The Cambridge created such a jump in dynamics, resolution, speed, and extension that I ended up upgrading the cartridge, line stage/amp, and speakers to exploit the 640P's potential.
You've been warned. :)