Ouch... I really like the sound of my (Nelson Pass designed) Threshold poweramp with my Apogees (Centaur Major). I'd suggest you take another approach and change the preamp for a tube amp. To my ears, Naim gear always sounds a tad bright.
Then again, it's all a matter of taste. For two K there are many poweramps available, especially secondhand. You can also 'tune' them a little bit by changing the tubes. Only problem of the Stages is the lowish impedance - not as bad as the Scintilla's, but 3 Ohm and a low sensitivity means a new poweramp has to be able to deliver some power. Make sure you test your new amp at home before buying.
Then again, it's all a matter of taste. For two K there are many poweramps available, especially secondhand. You can also 'tune' them a little bit by changing the tubes. Only problem of the Stages is the lowish impedance - not as bad as the Scintilla's, but 3 Ohm and a low sensitivity means a new poweramp has to be able to deliver some power. Make sure you test your new amp at home before buying.