Through the RCU801's menus you cannot assign volume punchthrough, the default is always TV and this cannot be changed unless you connect a JP1 and use the IR.exe program. RCA really blew it when this left volume punch toroug out!!
You can change the punch through to your receiver ("audio") on your RCU810 using a JP1 and IR.EXE (it take some work and basic electronics know-how).
Lots of info on this remote and the JP1 at
www.groups.yahoo.com, you'll need to join the group called JP1, there you can search the messages for RCU810 and also get the program called IR.EXE that works with the JP1 interface the you'll need to build. Failing that you'll have to use up your precious hlearning memory to learn your receiver's volume for each device.