Well, I think I FINALLY got my problem solved, and it only took 5 fans to do it.
I bought four 120mm computer fans from a guy on eBay. They're nice and quiet. I put 2 of them on the back panel, drawing warm air out of the cabinet. I put one fan directly on top of my 661. My receiver stays downright chilly now. I put one fan next to the PS 3, blowing cool air in. And for the hell of it, I put one of my 3" fans on the back panel, near the middle of the cabinet, pulling cool air into the cabinet.
Now with the door closed, the PS 3 fan doesn't go higher than the medium setting. It's still a tad noisier than I would like, but what are you gonna do? I think it's just a matter of the PS 3 not cooling as well in the horizontal position as vertical. I guess when it's vertical, the top vents do a better job of letting warm air out as it rises.