In any case, I have been wanting the mount my rear speakers since we moved into this house 2 years ago, but I knew that I didn't want to cut big holes in my sheetrock and try to divide the air space between the studs in the wall. Hanging speakers on the wall with a couple of screws was about as destructive as I wanted to be.
So, my father and I used the old SW-150 manual to learn all of the specifications of my in-wall 150's and convert them into MP-150s. The MP-150s were the "Plasma" or flat-screen version of the 150 and designed to hang flat on the wall along side a flat screen TV.
So, here are some pictures of the cabinets we made to convert the in-wall 150's to "on-wall" 150's.