I've added some more detail, it's finally starting to look like a real pin. I'm starting to feel sort of like an archeologist piecing together bones to recreate what a dinosaur might have looked like.
So I've split the cabinet into 3 pieces (not worried about the middle piece just yet). I decided to make the cabinet continue at an angle all the way back instead of flaring back to a square angle (There will be angled rails on the back to mount the legs to). The backbox ends up being really big, like 35" wide. Keeping the dimensions of the backglass at the same aspect ratio, it leaves about 4" of gap underneath, which should be enough space for speakers. I know it looks really narrow, but it's because the backbox is so wide. You may notice there are some square channels inside between the cabinets. There needs to be something to tie the cabinets together, and by bolting them together along the seams is the way to go.