You might want to check these out. They are not "in wall" speakers as much as they are "on wall" speakers. I know Klaus wouldn't sell them if they didn't sound good.
Scroll down to the bottom of this link.
http://www.shows.soundstagelive.com/shows/avtour2005/mtl_dly_apr03.shtml
Scroll down to the bottom of this link.
http://www.shows.soundstagelive.com/shows/avtour2005/mtl_dly_apr03.shtml