I dont think you can! I have had many systems that the tv or cable box is hooked up to the A/V receiver, and as all the line levels from the tv are at a pre-set level, (except the headphone output ) the tv volume purely controls the TV's own amplifier for its own speakers. And you ideally need the SPDIF optical output from the tv, and that is at a pre-set level. And seeing as that A/V amp is not HDMI compatible, that is out of the question too.
Hope this helps.
K