If no DSP then the voice on a Z4 is cabled as follows:

With TV:
From nav to TV tuner and then to the radio in the dash
TV tuner is located in the boot, mounted to the panel behind the seats (ie: directly behind the nav)
Without TV:
From nav direct to radio in the dash

In the radio, the audio is on pins 5 & 11 of X13649
Yellow/red is audio + (pin5)
Yellow/brown is audio - (pin11)
The wires are a twisted pair, easy to spot.

X13649 is the outer-most small 12p connector under the main radio connector
The wires will be easy to spot.