The only difference is that it doesn't give you the full power you would get from using a dedicated FireWire card. Since the sound card chews up a good portion of the power that is allowed the PCI port it is plugged into.
I believe if you read the documentation for audigy, it tells you the maximum power that the SB1394 port will supply to devices attached to it. If your CD-RW drive has it's own external power connector then you should have no problems at all.
I never actually installed my Audigy because the system I was going to use it in, I decided to buy the Nforce board, and am happily listening to 5.1 sound from the builtin sound card on that.