3DSoundsurge will be reviewing the HDA Mystique card, there's a thread on their forums about it.
The DAC is inside the Cmedia 8768+ chip that is the heart of the card. It won't sound as good as cards with the best DACs like EMU0404(AKM AK4395) or EMU1212M(Cirrus Logic CS4398).
The DDL feature is software driven, it's not hardware accelerated like the MCP-T does on the NForce2 mobos.
Drivers are very raw atm according to Chastity (3DSS reviewer and forum mod).
If you use the DDL feature, you bypass the DAC on CMedia 8768+ chip and use the DAC inside your receiver, thats the beauty of DDL. The Soundstorm mobos had crappy Realtek AC97 codecs providing the DAC, and by using the DDL feature, they get a big upgrade in sound quality when paired with a receiver with a good DAC.