Well, it didn't work. I painted the panel black, mounted my fans to it, but when I went to screw it into place, there must have been some type of interference between the panel and the cables. I heard this weird clicking that sounded like something shorting or electricity crackling. Moving the panel would sometimes make the sound go away, but it freaked me out so much that I just said screw it.
Even with no panel on the back at all, and the door closed, the PS 3 fan still kicks into high gear. The weird thing is that if I put my hand next to the PS 3 fan, I don't feel any hot air coming out. The fan is making noise, but it doesn't seem to be doing anything. I think I'll call Sony about that tomorrow. So I ended up putting a 120mm fan next to the PS 3, and that seems to have solved that problem for now.
And today, while watching a movie and leaving the door cracked, my cable box fan went into turbo! I think I'll move my lower fan up to the top, behind where the cable box sits and see if that helps.
I swear, I'm ready to give up. This has turned into a complete pain in the ***.