One of the reasons I think Oculus went with an onboard DAC is to precisely sync audio, visuals, and head tracking. Using a non-Oculus audio pipeline could introduce unpredictable timing and a worse experience.
That's an interesting thought but I'm not sure that's the case. Everything I've read about VR indicates that latency capturing and interpreting input are the biggest factors in the VR experience. If output latency were a major concern then I'm not sure they'd have chosen standard HDMI to carry the audio/video signals. The DAC on the Rift is simply to take the HDMI audio and output it.
One of the reasons I think Oculus went with an onboard DAC is to precisely sync audio, visuals, and head tracking. Using a non-Oculus audio pipeline could introduce unpredictable timing and a worse experience.