AC3 spdif output and stereo downmix at the same time

[CoreDump]

Hello,

I am building a PVR system around Mythtv.
I want it to behave as close as a normal DVD player or recorder, this means that when watching a DVD, sound must be routed through spdif (AC3) and stereo ouput (for the TV set).
This way I can run it without HT running.
I could not find a way to do it witout requiring an user action.

Thanks for any idea.