I had the same problem with my PS3. I have a HD cable box with HDMI out, a Sony DVD player with HDMI out. The Sony receiver STR-DG800 only has the HDMI inputs (sat/tv and dvd) and the HDMI is only a pass through port and will not decode audio.
I purchase a HDMI 4 port switch from Newegg (HS-41A0 http://www.newegg.com/Product/Product.aspx?Item=N82E16812168003&Tpk=HS-41A0
) to hook up the DVD and PS3 to the DVD HDMI and switch between the DVD player and the PS3. It took me several days to figure out how to make this work with the settings on the reciver.
1 the DVD player must use the coaxial in jack for sound on the receiver.
2. the PS3 must use the optical connection on video1
3. the sound settings in the PS3 must be set to PCM
4. set the sound setting on the receiver to the following
a. on the remote press AMP button then the MENU button, next press the down arrow to you see 5- AUDIO SET - then press enter.
b.set sound decode priorty to PCM
c. next scroll down to you see digital assign - press enter
assign VID1 OPTICAL to DVD ( this allows the pcm output from the PS3 to play through the receiver), next assign DVD to COAXIAL setting DVD to DVD (this allows the digital sound to play from your DVD player).
So when you use your remote and select DVD, you can use your PS3 or DVD through the 1 DVD HDMI port.