The Epiphany
During the Big Bang Kickstarter, it dawned on me that instead of everything over USB, which most devices were limited to only charging or Hosting, that Bluetooth would offer a far easier experience. By using Bluetooth for the Volume control and a Bluetooth receiver for the amplifier,the wiring to the tablet would be limited to just power.
Volume Knob
Going for the most minimal approach, I chose to attempt to drive just one MCU pin, and rely on an A/D converter to determine shaft direction as well as button depression. While it works, it's finicky. A direct, and digital approach would resolve those issues. Unfortunately I haven't found the time to rebuild it. Soon!