I don't know why, but I just randomly thought of this and I thought I'd share with you guys, despite the fact I was the one asking the question in the first place.
If I would ever encounter the sub cutout being too big, I think this is what I would do:
First of all, what I would have to do is bust out the jigsaw and actually make my problem worse... Meaning, the sub cutout I'd have to make wider. Reason is, if you use T-Nuts like I do, it wouldn't be wise for the T-Nuts to grab only on one side... So you'd have to actually make the already too big sub cutout actually a bit bigger. If you're confused over what my explanation is saying, then this would have to be one of those "see it to understand it" type things... Anyway, I would get another piece of 3/4 MDF to fit over the top baffle, but instead of making it the entire width I'd probably slim it down a bit. For example, say my box is 15 inches by 35 inches (which it is). What I'd do is, probably make the board about 15 inches tall (same height) but only about 20 inches wide. I would cut the edges of this board on 45 degree angles... that way I could sand the living hell out of it and it would look like the sub is protruding from the box.
It's just an idea I thought of, I figured I'd post so some folks here could have some insight if they ever ran into this problem. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif