UPDATE:
In an effort to find a resolution to the sound problem I continued my search and tried a few other .apk versions as I had discovered various posts about sound problems which various .apk's (including yours) implied to have a fix for.
In doing so I found an .apk which worked on my device (a few didn't) and it also put the sys.txt on the SD Card where I can edit it.
However there was still no voices searching the settings again nothing I did made any difference - so as an experiment I downloaded a free sat nav app from 'Google Play' and installed that to see what happened, and the directions were announced in that. Then I tried Google Maps again (pre-installed on the device) and suddenly I noticed there were spoken directions which were not there before.
So I tried Primo again - and voila it had sound.
Now this is where I get embarrassed.:o
As I pressed the 'Off' key on the device to turn it off I noticed that the confirmation window not only asked for confirmation that I wanted to turn it off, but it also had an option for 'Fight Mode' and also 3 icons at the bottom of the panel. One icon was a crossed out speaker, one was a speaker and the one in the middle was a small 'Smartphone' icon. There was a small bar under the speaker, and if I tapped the 'smartphone' icon the bar moved under that - and the sound for spoken directions disappeared for all apps. Moving it under the speaker again returned the sound
I still haven't found an explanation of the 'Smartphone' icon and how it is supposed to affect the device, but I guess that was the original setting and for some reason it was changed when I installed the second sat nav app.
Anyway, I now appear to be sorted - so thanks for your input.