Hello friend. Welcome to the forum, I think I might be of assistance to you here.
You see when I purchased my Axiom HT system I had already built my HT closet complete with a cut-out at the bottom for my EP800 to sit with only the grill sticking out exactly as you discribed. When I got it put together it looked fantastic! However, the bass was severely lacking!
After a long, hard fought battle to increase it's performance, I finally had to accept that the location was all wrong. Sadly, I didn't really figure this out until one day when I walked into the closet while I was listening to music, and the bass almost knocked me down! "WOW" I thought to myself, "so this is where all the bass is hiding out"!!!
In the end I wound up dragging the EP800 out and sticking it behind my couch. And the difference was like going from an EP150 to a full blown EP800!!! I would estimate the amount of lost bass frequencies inside that closet at something close to 80% (this is a seat-of-the-pants figure, I didn't have any sound level equipment at my disposal). I will admit that had the difference been closer to 50% I might have kept it in the closet just to keep the asthetics of the lay-out. But the difference was too night and day to ignore. I really wanted it to work underneath the TV, but it just didn't.
So now the ONLY way I would ever say, "go for it" to someone asking whether he should do something like this would be in a WAF scenario where the subwoofer either had to be hidden inside a wall, or there be no subwoofer aloud in the system period. It is at least better than not having a subwoofer. I mean you can go back and read my impressions of my EP800 and you'll see that it did improve the sound of my system a great deal. However after finding out how much I was missing out on, that's the only scenario I would ever personally give my approval to. If there is ANY other location you can put your subwoofer in, in your HT, try it there first! No matter how sub-prime it may be, it's still sure to be better than hiding it away inside a wall.
I hope my mistake can help you avoid making your own. Good luck with finding a compromise that will suit your needs.
