Hi I fitted a new Sony head unit to my 1999 A4 saloon non-Bose,as the old unit was looking dated(it was also an aftermarket HU). I have never had sound from the rears so came on here for help and found all I needed was a PS9- 404 to fix the problem, but it hasn't. If I fade all the volume to the rears you can just here it so there is something there, have I not done something right I'm baffled