Paradigm Studio CC690 v.4

Feeling the need for a large center speaker for a 64" Pioneer TV, I bought a Paradigm CC690 and placed it above the TV, at eye level. Pre/pro is the Onkyo Integra DTC 9.8 and the amp is a 7-channel Gemstone (200 wpc). Main source is a Direct TV HD receiver or Denon DVD. The center "voice" is driving me crazy, especially when the source is the Sat receiver. It sounds unnatural -- muffled and boomy at the same time. It makes little difference what setting I use on the pre/pro -- DD Ex, THX ultra 2, etc. When the source is a DVD, the center sounds better, but the voice from the cc690's tweeter and a 4.5" voice speaker below it are still strange, as if the tweeter and voice speaker were not working well together.

Could it be the Gemstone amp? Can anyone suggest a fairly good monoblock or multi amp for the center? If it's not the amp, what could it be?

Incidentally, my fronts are Acoustic Zen Adagios. Any stringed instrument sounds very very good with these speakers, although I wish they had more bass punch (as in drums).

Thanks.