Do you mean when playing TV back through receiver ... for example from Digital Free to Air receiver in TV using the AMP for sound ? 

I have TV plugged into HDMI OUT A and set the HDMI output to A only not A+B  ....A+B for some reason doesn't work.

Update... The manual does imply its an either /or a or B situation, however one way around it seems to be to use an optical connector from the TV to the AV and change INPUT MODE to OPT on the AMP MENU display via the front panel menu ... I don't think this is setup via the GUI  only as a LED front panel option via AMP MENU button.

Printing of the User Manual is a MUST for this box... then take a degree course