Youre welcome, using natural voice did the Trick for me...
I've tried all the voices that have "Natural" in their name, but they don't seem to be using TTS.
Perhaps its the option with "Street names" that I need to select, as I presume that the pre-recorded speech could not be able to announce street names unless it was using TTS ??
OK.
I can confirm on my Xtrons (Oreo PX5 GS) unit, that selecting the voice option, which includes the words "street names" (Its the first item in the list for me), that this switches to an external TTS app.
Initially the TTS didn's sound very good, so I checked the TTS settings and it was set by default to "Pico TTS" even though Google TTS is installed.
(note I thought I may need to install Google TTS, but it seems to have been installed already on my Xtrons unit)
Google TTS seems to be better than "Pico TTS". Its still not as good quality as the non-TTS voices, but at least it doesn't crackle. !
BTW. I on my phone there are a number of different options for Google TTS, including "Intonation" and an option to "Amplify speech", but these options don't seem to be available on my head unit, even though I checked and the latest Google TTS seems to be installed.
(though I will double check in case there is an update)
BTW.
I noticed that it seemed to take quite a long time to get a GPS fix, as the unit does not have an Internet connection, so I changed the Location settings, to only use the satellites, as this stops it waiting for the Internet to time out multiple times.
I think this speeds up the time to get a GPS fix, however it keeps nagging me to switch it back on (no doubt because Google wants to get my location data whenever possible)
PPS. I changed my Google account settings to try to stop Google collecting all my location data (GPS tracks etc), but I don't know how much attention Google really pay to the privacy settings.. Especially as it keeps nagging me now I have selected the GPS satellites only option, and its not attempting to use WiFi etc