With all due respect, very few have actually seen and heard the new-generation Yamaha AS2000 as they are scarce and seemingly expensive - until you hear one. You might be in for a small shock here. I have done some extensive listening with this amplifier, as well as with the NAD. The NAD is ALWAYS the proverbial contender in this price bracket and it is wise to audition it.
So, not to offend anyone, the NAD is very nice and has those great value-for-your-buck values. Its a great buy, like all Nad products.
But the SOUND, build quality (simply amazing) and overall package,(not to mention the stunning looks)of the Yammaha puts it in a different league, and it is actually a bit unfair to compare the two. The Yammy is so much better and more refined it is not even close - at least with speakers that can exploit its full potential.
Full disclosure: I have auditionned those amps with speakers that should usually be partered with 5K and up amps, and they clearly pointed the limitations of the NAD.
This may not happen with more average speakers and the differences between the two amps may not show as much sonically, but they are surely present and obvious. One thing for sure, even in the ''off'' position, the build quality and features of Yammy comes out way ahead of the NAD - and most every other amp in this price range for that matter.
I would rate the Nait 5 highly also - but it will run out of steam pretty quickly compared to the Yam, and of course has very limited features comparatively. I would say the Nait is a ''faster'' amp, but with a somewhat dryer sound and a (much) flatter soundstage, where the Yam is more authoritative and a touch smoother.