i have been reading this forum and me along with others wanted to fit a mk3 or 4 sat nav to our bmws which already had tv installed at the factory. after fitting the sat nav all seemed to work well,sound from radio and tv,satnav worked fine, but no voice for turn instructions.
my radio muted for a short time for the voice(which never happened just silence)and then went back to previous volume.
after a lot of reading,probing with meters and test light, i found the cure which worked.
blue multi plug from back of sat nav, branch pin connection 18(blue wire with brown stripe) and connect this to pin 9 (yellow wire with red stripe)of the blue multi plug that goes into back of tv tuner module.

then from pin 9 (blue wire with red stripe) of blue connector on back of sat nav, connect this to pin 18 (yellow wire with brown stripe) of blue multi plug on back of tv tuner module.
i did read in another thread a link to another forum where someone had the no sound issue on an e38. he connected pin 18 from sat nav to pin 18 on tv module, along with pin 9 to pin 9 satnav to tv.
i did this first but got a horrble buzzing noise instead of the voice.
swapped the wires and got a nice clear ladies voice.
hope this helps others.