If you are spending that much on a killer room and equipment, why not step up the speakers as well. Try out the PSB Synchrony's, Paradigm Signatures, or even B&W, DynAudio or Sonus Faber. Fairly expensive when you go a step above the Imagine's, but will probably bring about your greatest change other than going separates.
As for separates, there is always the Marantz av7005 mated with the mm8003 8ch. amp or the mm7055 5ch. and 7025 2ch. for a more flexible amp structure (better for 2 ch music I would imagine), or Onkyo separates that look promising as well. http://www.avguide.com/article/onkyo-announces-thx-certified-av-separates
As for separates, there is always the Marantz av7005 mated with the mm8003 8ch. amp or the mm7055 5ch. and 7025 2ch. for a more flexible amp structure (better for 2 ch music I would imagine), or Onkyo separates that look promising as well. http://www.avguide.com/article/onkyo-announces-thx-certified-av-separates