Any GTX460 + Onkyo TX-SR876 (or 906) users out here?

[THX-UltraII]

I just moved from the Marantz SR-5005 to an Onkyo TX-SR876 because I wanted to upgrade from Audyssey MultEQ to Mult EQ XT and could make a good deal on the Onkyo.

Tonight I fired up my HTPC in order to play a Blu-Ray movie. Unfortunately NO SOUND. I checked the Nvidia Control Panel and the audio properties of the TX-SR876 which was nicely showed by the Nvidia Control Panel. Next, when you click on the audio button in the Nvidia Control Panel you automatically are directed to the windows audio properties. The High-Def audio is set as default audio device. Next I cheched the properties of the audio device. I always select 5.1 surround and select TEST. Normally a pinging sound sequence is then heard from all the satelite speakers and subwoofer, but as soon as I click on TEST the amp shuts down and the stand-by button keeps blinking red. When I put it back on and try it again it keeps happening. Ok, no testing is what I thought, let s try Media Player Classic again: NOTHING...... no sound at all.
I know the HTPC is set up properly because everything worked ok on my older Marantz SR5005. There s also one more strange thing: when I startup windows with my Onkyo ON the Dolby Digital (red) icon is showed by the Onkyo. This also seems strange......

EDIT: When running my high-def Blu-Ray I said there is no sound comming from my AVR. To be more specific: nothing happens with the AVR. Normally you can see the AVR switch to eg. Dolby True-HD or DTS Master on it s display but that s not happening.

Also the problem is not Media Player Classic: this is configured properly because it works on my Marantz SR5005.

Setup:
- Onkyo TX-NR876 with latest MAIN firmware (1.05) and latest DSP 1st version.
- HDMI main as output to HDMI input of my JVC X30 projector.
- HTPC with Nvidia GeForce GTX460 with latest Nvidia driver
- Nvidia mini-HMDI output connected to HDMI1 input of Onkyo with a miniHDMI=>HDMI dongle=>regular HDMI cable.
- Windows7 with MPC-HC as player.


Something is not right here. Can anyone help?
If more information is needed please let me know.

[DragonFury]

is the control panal of windows set to the video card as a default sound ?