Time for troubleshooting
Locust,
OK, now that it sounds like you verified the speaker wiring is correct, I would do the following to try and isolate the culprit.
1) Double check your wiring one more time, just to be sure.
One more thought, please confirm you do not have headphones connected--this disables the speaker output. (see Manual p. 26)
2) Start with something simple like the FM Radio.
(This way the sound source does not require an external device--PC, XBOX, etc.)
These steps will walk you through using the SCENE "RADIO" button for FM:
----a) Ensure you have connected a FM antenna.
----b) Push the SCENE button for RADIO, it should turn the unit ON and set the sound field to 7CH ENHANCED. (see Manual p.24)
----c) Select FM Radio and tune in an FM station. Confirm "FM" is visible on the Front Panel Display. (see Manual p.31)
----d) Set the Volume to between -30 and -35 (Note: smaller numbers = louder volume)
----e) Cycle the Mute button on/off using the remote to ensure it is not inadvertently engaged.
----f) Confirm you are not in "Zone 2" mode (see Manual p. 6, display item #7 and/or Manual p. 4, button "C")
3) If you get sound from the speakers, the issue is with your 765's Audio Input Source settings or the XBOX's audio output settings.
(FYI: I know nothing about XBOX audio!)
4) If you do NOT get sound, the issue is still with your wiring and/or receiver.
I am hoping the wiring you described in an earlier post did not damage something.
Good Luck,
XEagleDriver