\rHI Johnny :
The output from your AVR is Pre amp only. You need a dedicated Sub woofer amplifier like our SMP250 That has a crossover built in but since the Yamaha RX A770 will output LFE (Low Frequency Effects) will bypass the controls on the SMP250. There are instructions in the manual for setting the controls of the SMP250 when you have a true LFE input signal.
Good luck
TL/4833\r