Dig the yellow..

My line of thinking for the menus is a little different, but not far from where you are. Fully transparent would be nice, for sure.

I guess in my mind, it's more like

-floating transparent texts on main/audio menus. For the main, there will be a motion menu.

As for popups, I think the ideas there are all good, but with 30+ subtitles, it'd be interesting to see how that works with just a bar or two above the main navigation.

In my head, I picture it being separate audio/subs menus with several rows, likely across 2. ..would prefer navigation to more choices across as few screens as possible.

The additional rows layout just seems possibly limiting for the # of tracks. I guess I picture more of a set of screens full of choices if that makes sense. With a set of psd's, I can show this better, I believe. Will post my draft capture of audio screen to give better idea. It is quite full, with all 21 tracks on one screen. I'm also aware of the graphic limits, which I ran into initially when using secondary background, but I think we'll be fine with just motion menu background(s).

Catbus - thank you for that info. It is as I feared ;) the audio is also vbr, at least the main lossless track is for sure. Guess we'll have to give it a try, to see what ends up working.