I'll be mounting my 52" LCD above the gas fireplace mantel (not an issue)
My concern is my 13 inch deep Paradigm center channel which to look right I need to install at least half of it in the wall above the fireplace. I could probably rest about 7 inches of it on the mantel but the rest would have to go inside the wall.

I'm not sure about the heat inside the wall or the distance I have to the gas flue before I run out of room. Has anyone mounted that deep inside the wall above a gas fireplace?

All the people out there with flat panels above the fireplace and no one has a built in center channel?:confused:

In my original design, I had a 50" plasma above the fireplace with the center ch. above the Plasma TV. But I moved the fireplace (yes...after framing) because of the heat temperatures being created near the TV.
I would check the manual to see exactly where the flue is in relation to the recess you will create in the front. My guess without knowing the make/model of the fireplace is the flue pipe is generally towards the rear of the F/P, but again, check the manual. Seems to me you should be OK but I would get a reading on the heat being generated at the mantle before making any alterations. I'm not sure about the heat within the wall recess, but I really don't think it should be excessive.

If your fireplace is masonry your s**t out of luck, bur metal you've got a fighting chance. How were going to run the low voltage and electric to the TV? Any way you look at it you'll need to do some kind of patching, so poke a hole in and take a looksie. As j-time correctly mentions, heat from the flue itself generally is not the issue, but the heat radiating from the fireplace opening is what you have to be careful with, ymmv.

I talked to the manufacture of the gas fireplace Majestic and they said as long as the speaker and wires are two inches from the flue I should be okay. I opened it up and everything looks okay in there. It should work I hope