Try a passive preamp with your Parasound amplifier. Do you have a source with a variable output ( bypassing the preamp )? Because of the very high sensitivity of the CW4s, you do not need the additional gain of a preamp, and a layer of noise and distortion will be eliminated ( IME ).
Better Amp for Cornwall IV's...
...Parasound 2250 v.2 / 200 Pre combo, which I own, or Denon PMA-1600NE integrated, which I don't, but I admire the build quality and appearance of? My Parasound is rated 275W into 8 Ohms / 400W into 4, while the Denon is 70W into 8 and 140 into 4. Of course, the Klipsch Cornwall IV's are quite sensitive and are rated 8 Ohms. Maybe more than which is better, which would you all prefer?