Thiel In-wall Speakers

I am getting ready to finish my basement and am upgrading my surround speakers. I am considering using Thiel in-wall PowerPlanes for the sides and a single on-wall PowerPoint for a mono rear. (An HVAC duct does not allow me to equally space two PowerPoints in the rear but I think one will be sufficient anyway.) I have CS6s for my mains and a SCS3 for a center. Would anyone do anything different given this limited info.

I have an all Thiel surround set up. 22's for the mains, SCS2 for the center and SCS's for the rears. Instead of using PowerPoints or PowerPlanes, I built pockets and recessed the pair of SCS's. I was able to recess them approximately four inches and they look great. The SCS's were built with 1" MDF with Oak Veneer and were designed to sit in a bookshelf. They sound great and one should be able to find a pair here on Audiogon for around $600 if they are patient.
I have an SCS for my center channel and I have been unhappy with the way it sounds. It doesn't cover the high frequencies well at all. Could my tweeter be out? I bought it used. It also has a boxy resonance in the lower midrange. Surely my tweeter isn't out!!!!! Islandflyfisher, do your SCS speakers have good high frequency response?

P.S. I am using Thiel CS2.3s for front and CS1.5s for rear.

My SCS's sound very natural and well balanced. I played music through them alone for six months as I was constucting my HT/Soundroom. I was amazed on the quality of sound I got through them. I will say that I am running an honest 300 WPC with good quality cables. How much power are you running to them? I would attempt to try testing your SCS by playing some good reference audio and I'm sure your ears will tell you if you have a blown driver or two. Thiel manufactured the SCS so that it could be placed on a bookself so the cabinets are constucted out of 1"MDF. They should not sound boxy at all.
Does anyone have Powerpoints or Powerplanes and use them in a multichannel music environment. I'm concerned that their limited freqency response might not work well with SACD or DVD-A.