Hit the HOME button five times, then hit fast forward, the down button, rewind, down, and fast forward.
(home x 5, >>, down, <<, down, >>
choose RF remote menu
choose IR transmit menu
choose Enable Querying AVRs (instead of TVs)
You can always go back later to toggle this option back to normal.
When you go back into the normal settings menu to set up your remote to control your TV, AVR brands will be substituted in for the TV brands you'd normally have there. If you succeed in finding a match for your AVR, the volume, mute and power buttons should control your AVR.