I don't see an option for "DVD Audio" in my copy of Toast...
DVD Audio is a real format, though, so it may be that your PowerMac's SuperDrive is slightly different or "better" than the SuperDrive included with the PowerBook. If you could post the model numbers and makes of the drives here, I'm sure we could look up the exact formats supported by those particular drives. My bet is that the drive in the PowerBook doesn't support DVD Audio format.