You have a great option,the NHT 2.9's can really sing with good power behind them. I will be looking for your results. Good listening.
Since you have the SA-3 amp try it I have had two running on a pair of 2.9s with great results. The Classe you have is 100 watts at 8ohms and double downs at 4 ohms. Given the 2.9's are 6ohm speakers I take it you'll have 150 watts powering either the full range speaker or just the mids and tweeters.
I use to have the 2.9's and powered them with a variety of amps. The best I heard the 2.9's sound was with a pair of VTL MB450($9,000) mono blocks powering them biwired. I did not have the SA3 amps to compare at the time although the SA-3 amp provided excellent room tuning capibilities.
As the previous poster commented the 2.9's thrive on clean high current power.