This would be easy to do and you could always add a DAC later. But, I have read that the sync between the audio and video can be a problem.
Is this really much of a problem?
I haven't found that to be the case, and I watch/listen in that mode
4 8 12 many hours a day. Or at least, it's not any worse than doing it any other way. One thing that is a little off about most if not all digital TV is that the sync is not that great even in the best of conditions, and even if you just use a plain old TV with nothing attached. And it seems to vary from program to program and the way it's acquired. The worst are old TV shows with sound processing applied. Sometimes there is some sort of processing that is intended to remove the hiss and other noise reduction, and when it's not done properly, you can hear it both "breathing" as the source level changes, and causing lag that gets it out of sync.
You can hear the same thing in many low-data-rate digital sources. HD Radio, for instance apparently does something similar because you can hear the background noise level jumping around based on the signal levels. Of course there's no sync issue in that case.
But I don't notice any additional lag in the case of the external DAC, at least not in the Insight+.
Brett