After *much* searching and some trial & error, here are the DirecTV RC64R remote control codes for my living room.
To enter codes, slide the selector to the unit control (AV1/AV2/TV), hold MUTE and SELECT, and then enter the code.
Panasonic CinemaVision – #10250 (TV)
Yamaha HTR5240 – #30176 (AV2)
To enable stereo audio controls, select AV2, hold MUTE and SELECT, enter “993”, and press VOLUME UP.
To disable the TV audio controls, select AV2, hold MUTE and SELECT, enter “993”, and press SELECT.
For help in setting up a DirecTV remote, check this device code search tool.