I posted this on the Windows 7 Extenders forum and I did not get any answer.

I bet that the same happens with Vista. Can someone using the XBOX Media Center help me?

I have a XBOX 360 Arcade connected to my AV receiver via HDMI.
The XBOX Media Center is connected to my Windows 7 Home Premium HTPC.

When I listen to a song or watch a video using the XBOX Media Center, the volume is low (more or less 20 dB less of what I get from other devices, HDMI or optically connected to the same receiver and playing the same media).

I cannot find a way to raise the volume in the XBOX Media Center to the original level of the source media.

Interestingly this problem does not exist with the XBOX 360 dashboard player.
If I listen to the same songs or watch the same videos with the XBOX dashboard player, the volume is OK and matches what I get from the other devices connected to the AV receiver. The dashboard player has a volume control button. The volume was initially set at 30% and I increased it to 100% to match the sound level of the other devices.

Before answering that I could increase the volume on my AV receiver, please consider that I am using a HDMI connection and that something between Windows 7 and XBOX Media Center "digitally" decreases the original volume of music and videos. Raising too much the volume on my AV receiver results in a higher noise level and much lower overall sound quality.

How do I increase to 100% the volume of the XBOX Media Center sound?