[popcornmix]

Playing using either DVDPlayer or PAPlayer works with HiFiBerry. But dual audio output isn't working (I'd like to play out both HDMI and HiFiBerry). OMXPlayer plays over HDMI only, even when output device is set to HiFiBerry.

This is using standard the xbmc ActiveAE audio engine, so it will do what that can do (i.e. no dual audio until xbmc adds that as a standard feature).
It is also paplayer and dvdplayer only.
omxplayer runs the whole player pipeline on the gpu which has no knowledge of alsa devices.