Yes, we should have the TV information. Your receiver should be delivering a signal to be amplified, through the RCA connectors, if connected as I mentioned above AND according to your manual - see link and pasted info below. You are basically using the TV's amplifier and speakers, just as you would use any other power amplifier, which will work. You MUST configure the TV for analog audio input for that A/V input. Did you
turn up the TV volume as well as the receiver's? The TV's volume
must be turned up maybe 3/4 of the way.
https://manual.yamaha.com/av/18/tsr7850/en-US/3832211851.html
"When connecting an external power amplifier (pre-main amplifier) to enhance speaker output, connect the input jacks of the power amplifier to the PRE OUT jacks of the unit. The same channel signals are output from the PRE OUT jacks as from their corresponding SPEAKERS terminals."
"CAUTION
- To prevent the generation of loud noises or abnormal sounds, make sure the followings before making connections.
- Unplug the power cable of the unit and turn off the external power amplifier before connecting them.
- When using the PRE OUT jacks, do not connect speakers to the corresponding SPEAKERS terminals.
- When using an external amplifier that does not have the volume control bypass, do not connect other devices (except the unit) to the amplifier."