I have the Ah! 4000 w upsampler. The upsampler definitely brings out more detail up top. If you have a lot of rock CDs that tend to be bright to begin with, it can be a rough combo. The Ah! without the upsampler is more foregiving in this area. However, with decent mastered discs, I think it makes a decent combo. Can't give you relative merits vs the NAD, though.
Doug
Doug