center channel problem

I have a new home theater with thiel 3.6s as my fronts, marantz preamp, and parasound 5250 amp. Center is a thiel scs3. i'm very dissappointed with the scs, boxy and muffled. Dialog is uninteligible. Any thoughts on how to improve the center channel or a good center channel to match the 3.6.

BTW I tried the 3.6 in the center and it sounded great (but covered half the screen).