Htpc with Ubuntu 10.10 audio output issue

Ok I have an htpc running Ubuntu 10.10 . I have my video hooked up to an Epson 8350 projector with an hdmi cable. The video is working fine. Now for the audio out I am trying to run it to a Bose lifestyle 28 system the problem with this is the Bose does not have a hdmi input or output. It does have spdif out and inputs, which I have an spdif out on my computer. Is there any way to get my sound from computer to the Bose and out the speakers using this setup or is there some other way to possibly do this. Thank you any help at all is appreciated.