I noticed that there was an alternative call using tremor commented out in /usr/bin/MediaCenter, line 281. I enabled this line and disabled the next one (with oggdemux). Now the oggs are playing, although playing them uses all the CPU resources. But I find a bit choppy playback more tolerable than the player crashing whenever the random play chooses an ogg file

EDIT: I noticed this morning that when using tremor to play oggs, the player doesn't recognise when the song ends. This means that it doesn't automatically change to next song and the Play/Pause icon shows as pause. As this happens only with oggs, I can live with this. Maybe I should start learning python and how gst works, in order to find a better solution for 770.