I’ve just published Volume-AlpsRK16814MG, an open source hardware design that integrates a high-quality Alps motorized quad potentiometer with an H bridge. The design lets you control the motor’s direction using two logic-level signals: VOL_UP and VOL_DOWN. The fact that it’s a quad pot means you can use it to control regular stereo volume by ignoring one of the dual gangs or a differential stereo signal.
Here’s the schematic* to give you an idea what it’s doing. Gerbers and PCBs are available at OSH Park.
*Subject to change!