Hope this helps: How to reset the SR6006Microprocessor reset (p. 150 Owner's manual) - Press and hold the Zone Select/Display buttons while powering on the AVR ......release 4-5 seconds later
Network reset - Press and hold the M-Dax/Display buttons (resets network card and does a microprocessor reset) If you need further help, reach me via phone at https://www.6ya.com/expert/timothy_c6f309c0f75b6f43
Try switching the speakers over. If the sound now comes out of the faulty speaker the amp is faulty. If it doesn't the speaker is faulty.
If you can't find a replacement speaker, then buy a new pair of speakers. Match the ohms found on either the unit or old speakers with the same. The watts of the speaker can be the same or higher than the original.
First swap wires on the input and see if same side has a problem. If not then input wires or jacks causing it. If wires swap doesnt do anything then switch speakers with wires. If that doesnt work try to clean speaker connectors but there is a big chance that amplifier need to be repaired