Computer DVD drives pass all available data, so there is no particular need for a drive to "support" surround sound. Assuming it can play the disk's format (and it does) then exactly which data it can decode and play is related entirely to the software or (soundcard) hardware.
For example: you can't play DVD-A disks on a Mac* as of today, but the drives pass the DVD-A data. It's because there is no decoder available yet (but there will be) to deal with the signal.
Similarly, if you have a DVD player on your Mac and a soundcard with the digital (optical or coaxial) output, it will send all available audio (it supports up to 8 channels) to a surround sound hi-fi reciever.
* Well, you can. Virtually every DVD-A disk made is created on a Mac, but these pro-level tools cost $25,000 for the software. For us mere mortals, we'll have to wait for a consumer playback program that can decode the data.
What does M-Audio say? They're the guys selling you the soundcard/USB audio device, and that's the only part that matters.
If you go to M-Audio's Sonica site, you will see a link to the VLC player that supports surround out (Apple's DVD player currently does not pass the signal, but it is expected to be upgraded to do so).
From M-Audio's readme for the VLC player:
"... To enable surround sound output, choose "AC3 over S/PDIF" from the "Audio" menu. ..."
The S/PDIF output is another way of saying any soundcard with a coaxial digital output. What the Sonica adds is AC-3 decoding; if your multichannel reciever has an AC-3 decoder, you don't need the Sonica.
Similarly, the Revolution privides up to 7.1 (another way of saying 8 channels) of sound out via it's S/PDIF output, and 4 channels of surround out directly to 4 powered computer speakers. This card has the decoders for DTS, Dolby Digital 5.1/EX DVD 6.1 in hardware.