I agree that the first step is to launch the NAD amplification out the window. Sorry, but I have never heard an NAD amp that I liked and they all have the same problem you are talking about, in addition to other worse problems. I have heard the CM 2's on several occasions and in my opinion, the metal dome tweeter is just fine. These speakers have some other more subtle problems, but an etchy high register is not one of them. My recommendation is to look into amp, cables and source.
I have had good luck with the Acoustice Zen Epoch speaker cables and WOW interconnects. These smoothed out some etchy highs that some other cables produced in my old system.
As for an amp around $500 that has a less etchy sound, you may try a newer model (last 2-3 years) B&K integrated. This is the best I've heard at this price range (used), but it may still not be enough. I have heard some Linn amps that are very good, but I think they may sound best with Linn speakers using the AKTIV crossover. I don't think the Rotel should sound terribly harsh with the right cables, but I have not heard many of their recent offerings. I recently heard an Audio Refinement preamp/amp combo and was very impressed with the smoothness of the sound. The system was using Analysis Plus Oval 9 cables and similar interconnects. However, this system was also fed with a good source:
Even after an amp and cable change you may end up looking at the source. The system with the Audio Refinement amplification was fed by a McCormack UDP-1 universal disk player. What a GREAT system, but the disk player itself was over $3000. My own older system had a Magnum-Dynalab MD-308 integrated amp and the Acoustic Zen cables I mentioned earlier. The sound in the higher registers was still etchy on some (definitely not all) poorly recorded CD's, but I believe this was the fault of the source, a Denon DVD-2900 universal disk player and of the original recording. While detailed, the Denon was just not as refined as the rest of the system. The McCormack UDP-1 would likely have made a huge difference in the sound, but at a much higher price.
P.S. I am selling the MD-308 for just over $1000 if anyone is interested