Thanks all.
Here's more pics of work on the backbox (grrrrrr).
I started off wanting to do a 1/3 sized 1/2" thick board covering JUST the DMD and speakers, then drop glass down to that and cover the backglass monitor. The seam in the middle was the toughest thing to figure out, and I think it would have been really hard to make look good. (you can see that mocked up in the pic)
Sooo, I cut a full size 1/2" sheet to cover the front, put grooves in the sides and bottom of the box, then slid this sheet down in there. After painstaking measurements with the monitors locked down, I started routing out the holes in that sheet.
I kind of like the way it looks. I'm going to do some paint and artwork on those surfaces eventually. I wish I would have tilted it forward slightly. I made it perfectly upright (I slapped a level on it in one pic to show that) but in person it has the illusion of being slightly slanted back (because of the forward sloping sides).
Anyway, my main point I reached was "why use glass/plexi" at all on the backbox? It made sense on a MAME cab, when you're right there in front of it, but this is pretty far from the user. And besides, our TVs are all "uncovered" in the house - I play XBox 360 with friends in front of an "unprotected" big screen all the time, no protection isn't a big issue. (It certainly would be in a public place, however.)
If I cover the exposed frames and everything with a bezel or with wood like I have here, shouldn't that be enough? Am I missing something in my logic? If so, I will put a full 1/8" sheet in front (I allowed space for that in the channels I routed) or maybe BEHIND the front piece just cover the monitors.
Does that make sense?