Yes - We run the ASUS P4C800E Deluxe MOBO with S/PDIF out to a DSE 5.1 amplifier and it works just fine with PremPro 1.5.
You will not be able to listen to 5.1 audio from Premiere's Audio Mixer unless the audio is AC3 or DTS and your motherboard will allow compressed audio out it's SPDIF port. AC-3 and DTS are delivery formats and not meant for mixing/editing. I don’t think this is what you want.
If you are doing surround sound you will need to have a sound card that supports VST ASIO drivers as well as has at least 6 outputs.
Community content is available under CC-BY-SA unless otherwise noted.