I tried to setup my HTPC last night. My intention was to connect the graphics board to the 990 via DVI. The output is then routed to the TV (Sony 60'' XBR2, 1080P capable) through Component. The sound signal should run from the HTPC to the 990 using optical tosslink from the motherboard jack into OPT1 input on the 990.

What did work on the first try? Well, nothing. I know that the PC is sending video signal as I had it connected to a CRT monitor first and I activated the optical out on the MB in the Vista setup.

My question is: What am I doing wrong?

I might be using the wrong resolution for the video signal but I don't anything but a blank screen. Even more supprising to me is that there is no sound (start up jingle) as I used the same input on the 990 for my CD player. I apologize for my ignorance and any feedback is welcome!

The 990's DVI switching is a pure pass-through, meaning that digital video inputs are not converted to analog and analog aren't converted to digital.

Gonk,
if I understand your comment correctly, I would have to connect the DVI out of the 990 to a HDMI input on the TV to get a picture on my TV, correct? Any guess if this would look better than connecting to the VGA input of the TV? I read in some forum that the VGA input of the Sony's isn't that great, hence I decided to use Component (which obviously doesn't work) or HDMI.

Yes, you would need to connect the 990's DVI out to an HDMI input. As VGA and component are both analog while HDMI and your display itself are digital, I'd certainly look at using an HDMI input if you have one. It's likely to yield the best picture quality of the three inputs.

For whatever is worth, I have a working Linux HTPC connected to my system sending video via the 990.

I have an ATI Radeon X1300 video card with DVI output going to the 990's DVI-2. I am using the USB port for sound (for now). The 990 is connected to my EDTV plasma monitor via DVI connection.

In my opinion (and in my setup), the RGB connection looks about the same but the DVI connection's colors seem more intense.

I believe the sound issue could also be software related. You might need to tell your driver (or Windows) what device to use for sound output. I use Linux OSS and had to specify /dev/dsp1 for the sound to be sent out via the USB device.

So I ordered a DVI to HDMI cable from Bluejeans and I guess video is taken care of now.
Yesterday I hooked up the HTPC to my 990 and actually connected a monitor (24'' wide-screen SUN CRT, ~120 lbs.!) to it to see if I can get at least the sound to work. The MB (Inter Extreme D975) has an optical out onboard which I activated. The sound control under Vista indicated output when playing a CD. Also, light was transmitted by the tosslink cable. However, no signal came through?! I deactivated the onboard optical out, installed a sound card (Diamond Extreme 7.1) and connected, after proper activation of the SPIDF out in the device manager, to the 990 via coax. This sound card works without problems in my XP PC this way (connected to a Sony HT receiver). Again, nothing! Sound control in Vista indicates output when playing a CD but no music coming through the 990?! Vista claims that all devices and drivers are working properly. Am I just stupid? What am I missing here? I want to give it another try and download a new BIOS and sound drivers for the MB and/or eventually try to use USB for sound output. Maybe someone here can walk me through getting sound signal through USB. Would it be the same quality as using tosslink/coax digital cable?
Thanks for everyones help!

The USB connection will not carry a Dolby Digital or DTS bitstream, so you probably don't want to use it for a home theater PC.

Unfortunately I've not ever used a digital audio output from a PC, so I don't know what the various traps can be. What indicators are lit up on the 990's front panel when playback is active on the PC? Does the "Digital" indicator blink (which would indicate no signal present)?

Gonk,
at least USB would give me the chance to listen to my CDs while I work on getting the other issues resolved. I will try USB later today.

With respect to the 990 front panel display indicators: I can't really answer that question (yet) as I have the display turn off after 15 sec. I will monitor this also later today. Thanks!

Wondering if this issue was ever resolved. I hooked up an older laptop to the 990 via USB and have had success listening to CD and internet radio. Have just ordered a new computer with SPDIF via the motherboard and was hoping to use this connection instead. Has anybody had success with this type of connection?

I don't know what the final resolution was for Benson, but SPDIF should work just fine with DD, DTS, and PCM stereo. It's dependent on the PC's sound card and drivers properly providing that data, however.