In response to cnlevo on how to hook these up, you just hook your 3 jacks to the 3 analog out ports on the devices, then, for the:
1) Sonica, hooks to the computer via USB
2) Firewave, hooks to the computer via Firewire
3) Creative Decoder DTS-DDTS-100, hooks to the Mac Pro via optical digital out with a Toslink cable.
Thanks, jamil5454, for mentioning the Creative Decoder, I knew I had heard of something like that, but I couldn't find it.
I think the Creative decoder is the better option, if like Jamil5454 says it works with the Mac Pro (don't see why not), since the Sonica Theatre has been discontinued. You can find the Sonica at some retailers sometimes, but M-Audio stop making them.