Jeff,
Not sure if you are still watching this, but this is where I am,
I got volume control to work within the tablet, in particular:
1. Changing volume via hard buttons on side of tablet changes volume for the tuner and the tablet
2. Changing volume gesture from GMD gesture control changes volume for the tuner and the tablet
3. Changing volume via buttons I have built into the app changes for the tuner and the tablet
Also, I am nearly done with the ability to add an arbitrary number of presets (give me another day or two).
To eliminate the raspberry pi I am going to try to play with a bluetooth to RS232 converter, I just need to find the pinout for the mini din.....if you have seen one laying around it would greatly speed up the implementation.
If we get that last piece all you will need is (2 of which you already have):
1. Tablet with my APK
2. Bluetooth dongle
3. The HD Radio module
We are very close!!
As a bonus here is a screenshot....the gray area at the bottom will be where the presets row is....you will be able to scroll horizontally to see more presets