The play/pause, etc. buttons wouldn't necessarily have to be on each screen, I didn't explain my thinking very well before, what I meant was, for instance, when you have media playing, or are on a phone call, etc. If you're navigating screens outside of the control screen for the current 'audible activity' (ie. watching tv, listening to music, on a phone call), that space could be useful to place relevant controls for that 'audible activity' so that you could do things like drop the call, play/pause, maybe place light/volume controls in that space, just trying to think outside of how we currently do things in the UI to update the functionality while you're working through this. Personally, I think this would make the experience much nicer. I was thinking about the popup dialog too, that area could be a general information area of the screen so that when you have media playing, etc. that information could be shown there, and when a popup dialog needs to display, swap out the information...just a thought. I'm one of those people that likes for things in the UI to be extremely fluid and symmetrical, I also like for things to be sensibly placed with pre-defined standards so the user can anticipate where certain controls will be on the screen without having to hunt around each time they see a new screen.
Again, you're doing great work, keep it up!