After many tests on android Car Multimedia with iGO with settings in sys.txt

navigation_audio_stream=4

;STREAM_VOICE_CALL - Value: 0
;STREAM_SYSTEM - Value: 1
;STREAM_RING - Value: 2
;STREAM_MUSIC - Value: 3
;STREAM_ALARM - Value: 4
;STREAM_NOTIFICATION - Value: 5
;STREAM_BLUETOOTH - Value: 6
;STREAM_DTMF - Value: 8

The result was that the radio sound did not pause when the iGO gps gave commands
but that both the radio and the iGO gps could be heard at the same time but with a low voice of the iGO gps
The mix was not bad but the problem was the low voice

With settings in sys.txt

navigation_audio_stream=5

;STREAM_VOICE_CALL - Value: 0
;STREAM_SYSTEM - Value: 1
;STREAM_RING - Value: 2
;STREAM_MUSIC - Value: 3
;STREAM_ALARM - Value: 4
;STREAM_NOTIFICATION - Value: 5
;STREAM_BLUETOOTH - Value: 6
;STREAM_DTMF - Value: 8

The result was to pause the radio and only hear the iGO gps in each of its commands with a very loud sound which I reduce with the sound bar

If anyone has the sys.txt
with navigation_audio_stream=5
so that it has a mix and a loud echo in iGO without pause
Thanks