The correct way to pass paramenters is using a pipe (|):
PATH = C:\Program Files\Karens Replicator\PTReplicator.exe|mp3
The space and Quote also works because of the way windows handles execution commands, although the correct way of doing it would be:
PATH = C:\Program Files\Karens Replicator\PTReplicator.exe" "mp3
I'm assuming this sync is to transfer files between an external device and the PC, because RR doesn't require syncing for Tags..