@pierrrre,

The bottom line is there no GPS app that works 100% of the time.
Even TomTomGo has voice problems for a lot of users over at the TomTom Forum.
The fact that you are even installing it on Head Unit is a problem in many ways.
Even that it is not supported by TomTom.
Have you tried it with mirror link rather than on the head unit direct.
Or try the new TomTom NDS app which was made for Toyota in South America.
It works with mirror link too or you can try to put it on your Head Unit.
But again it is not supported by TomTom.

With the TomTom NDS app you have Audio output to pick from.

Music channel
Voice call channel
System channel
Notification channel
Alarm channel
Ring channel


One of theses channels should work for you that will not effect the music from what ever app you are using.
Plus check with the music app you are using there are user's who would have the same problem and maybe they have a work around to.

You can find the TomTom NDs app here too.

As for you weak WIFI you can always add a TP-Link to your WIFI to extend the range.
I use the TP-Link RE400 it even gives my WIFI in the parking garage of my apartment.
Plus 1/2 down the street I have coverage too.
They do not cot very much.
That way you save on you lawn...........