The voice you hear while navigarion is another matter.
That is TTS voice, every navigator has it. We are speaking about alert .wav file. It is not sure a navigator can handle it.
StreetPilot for Android devices doesn't handle any file, nor .wave, nor .mp3 for example.
I guess that is the problem.
No solution for that.

Inviato dal mio HUAWEI P8