That is correct, none of the analog outputs are necessary, just digital and USB. I will try your file tomorrow.
Vortexbox uses MPD as a local player but the GUI is Squeeze Center so I'm not sure how things are routed. The routine that has worked with ALSA is to set output to "hw" in the Vortexbox GUI and putty in to alsamixer and turn on my SPDIF output.
MPD makes these suggestions: http://mpd.wikia.com/wiki/Configuration#OSS
I'm not sure how our changes are going to affect network music streaming. When I have "hw" as output SPDIF sounds great on hard drive music but the built in Internet radio develops frequent ticks that sound like very high jitter. The internet radio works without ticks with output set to "default" but the SPDIF output is reduced to pure mud with very poor sound on hard drive music. The "hw" setting also introduces gaps between tracks that you do not have on USB output.
These are the problems that are pushing me to try OSS4.
