If you look at the DVD player, you'll notice the Dolby Digital logo. It stands to reason that it MUST be using the AC3 Stream, or if its not then its merely using PCM, which is nothing to do with AC3 and the logo shouldn't be there. Which then asks the question, why is it there? OS X or 9 has no method at OS levels to get this stream out, say to direct it over either FireWire or USB. If a stream can be supported by the OS, at a mere 640KBps I suspect a simple USB device is all that is needed to produce a coaxial AC3 connector. No fancey amps or PCI cards. That means even a iMac could potientally become the center of a great Home Theater!
Soundblaster Live for the Mac provides a Digital Audio out capable of driving 5.1 sound straight off the DVD through either Cambridge Sound Works' "Desktop Theatre" line or the Creative Labs' "Inspire" series.
The implication on Creative and Cambridge's webites is that Dolby Digital (AC3) signals will pass through and be converted by an out-board amp that comes with the speaker packages.
Total cost appears to be under $500.00 total for 1 centre at 21 Watts, 4 surrounds at 7 watts each and 1 30 watt Sub. Cambridge Sound Works' 3-piece systems are enough to fill a 15'x30'x8' room.