I don't know about this guys.....let me explain.
I was at a party the other day, up in the British Properties (land of nice houses for BC). He had a paradigm system and the fronts and subwoofer were in cabinets below the tv, 6 inches off the floor or so. I think the sub was a PDR 8, which is rear ported.
I must say, it sounded DAMN nice in the cabinet. I didn't compare it to outside, but it sounded like a subwoofer usually does. Stinking loud, we made the floor shake on the third floor.
I know your going to say " But sheep, my calculations say that this will never work, and it will sound like crap, and be quiet!!!!1111"
I heard it, its sounded damn nice, give it a try, and see if it works.
Sheep