Hi,
Interestingly, Set_SoundDriver checks that its parameter is not an empty string, so this doesn't work:
if [ -n "$1" ]; then
...
Since the behavior of Wine when the driver is set to an empty string is documented, it looks like a bug. I wonder if this test has been added as a hardening attempt, or it prevents some specific problem.
Anyway, even if the test is removed, it doesn't help you for the time being, lots of PlayOnLinux clients with this test in place will be used for years. The next best thing you can use for the moment is the rest of Set_SoundDriver code:
[ "$POL_OS" = "Linux" ] && POL_Wine_UpdateRegistryWinePair 'Drivers' 'Audio' ''