Optoma HD-3000 User Manual page 73

If you have an HDMI equipped AV receiver and wish to send the audio signal to the receiver,
but utilize the HD3000 as the video source selector:
1) Connect the video sources to the HD3000.
2) Attach an HDMI cable to the "To AV Receiver" port on the back of the HD 3000. Connect
the other end to your AV Receiver. This will allow the audio signal to be controlled by the
AV Receiver.
3) Attach a 2nd HDMI cable to the AV out port on the back of the AV Receiver. Connect the
other end to the "From AV Receiver" on the back of the HD3000. This will return the video
signal in a "pass through" mode.
4) Finally, connect an HDMI Cable to the "To Display" on the back of the HD3000. Connect
the other end to your display projector.
Option 
Using HD3000 as video source selector and directly connecting the video source to the AV
Receiver:
If you do not have an HDMI equipped AV receiver, to ensure proper audio connections, you
will need to directly connect the Audio out from the Video source to your receiver. The
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HD3000 User's Guide 9