I finally built my HTPC and install Ubuntu 10.04 last night on it.
My motherboard has both the optical audio out as well as the coax one. which one is preferable to use?

I also have a Sony 5.1 Dolby Digital/DTS Surround sound decoder that I'm outputting the audio to.

I tried both audio connectors the coax and the optical and in Sound Preferences-> Hardware, under the Profile drop down box, I am unable to choose Analog Surround 5.1 Output + Analog Stereo Input. I'm guessing this is the right profile to use right? I only hear sound when I choose Digital Stereo (IEC958) Output but i'm concerned that this is not true surround sound output.

Please advise. thanks!