I did try that some time ago and notice the same thing regarding the sound!
How did you manage to have internet on the device? The last time that i have tried that, i was unable to connect using bluetooth.
regarding the sound, once mio4 is installed to an sd card (only works stable this way) cold boot the satnav with the sd card out, and then insert the sd once the nav has booted fully, it will then load mio after the seat app has installed the radio drivers on boot (this gets missed if you boot mio from cold) you need to add the user shell.exe and navigation.exe files to the run on boot menu in mio otherwise the seat service gets closed.
now you must add a 8 hour silent mp3 to the media/music folder that mio creates, seats media player goes here first (put normal music in another folder so this happens automaticaly when you press the nav button on radio).
now you should find all the audio from windows and movie is directed through the radio, and the nav button on the radio is back!
im making a video for the bluetooth as it would take an essay to write
how to do it!
Here:
https://www.youtube.com/watch?v=481_pQNo0HI
another note on video playback, i studied the video demo installed by mio and encoded some films and family guy etc and the format is very fussy to get good stable playback, i used these settings:
Video codec: mpeg4
Frame size: 480x272
Video bitrate: 1024
Frame Rate: 25
Audio mp3 2 channel @ 128kbps
these settings gave the best smooth playback without stuttering and pretty good quality picture (probably best possible with this amount of ram and cpu speed)
Mat.