Thanks, Rick. I really wish I could keep the back and sides open, but with only having the aluminum face plates on the front of the cabinet, they won't block any sound whatsoever from my furnace, HEPA, and HRV; it was loud prior to having that hole in the wall.

I unfortunately need something to limit the amount of noise coming into my entertainment room, and building a cabinet around the back is the only way I think I can achieve it. It did cross my mind that I could try to fill the gaps around each component with that sound absorbent insulation from Roxul, but I don't think that it would be a good idea. I also thought about using something other than aluminum, like wood for the face plates, but it would protrude too far, as everything is set up to allow just enough room for a thin piece of aluminum.

The only reasonable argument for owning a gun is to protect yourself from the police.