Amp for NHT 2.9's

You didn't mention a price point but some to consider are the Belles 150A, Belles 350A, and Plinius SA-102. An Aragon amp might also fill the bill.

I personally really like Atma-Sphere tube amps. Paired with some Zero Autoformers (provides optimal impedance match) I think you would be extremely impressed.

I would definitely take the opinion of someone like Cytocyle seriously. There is absolutely NO substitute for experience.

The amps I have mentioned cost about $1,000-$5,000 used.

I owned NHT 3.3's and if the best upgrade you can do is buy a NHT SA-3 Sub amp and actively biamp those speakers (since the base of those 2.9's is just like NHT's older 10" sealed subs) That is actually how this amp was designed. I used Transparent Cabling and found the Cardas to be too dark on top for the tweater. I would actually recommend one of the larger current Rotel Amplifiers, the Classe was too harsh with the Aluminium tweeter on my 3.3's so I would stay away from them unless you can listen before buying.

Make sure you butt those speakers against the back wall for proper bass corner loading. That is how those speakers were designed. also the listening position should be between 1.3 and 1.5 the distance between the speakers.

As far as cables go: I agree with Jimmyrod. Buy Cardas or Transparent.

As far as amps go: I owned Bryston, Classe, and ultimately found the best fit with the Mark Levinson no.27 or no. 23. These two Levinson's warm nature and the cardas interconnects made for a very nice combination!

Best of luck.

I would look for something like a Classe CA200 or CA300. Overall I thought Classe/NHT had the best match. There are others, but for the $$ I'd go there. Also look for Cardas cables and or Kimber 8TC.

Good luck.