Maybe stopping PulseAudio is excessive too.
You may use this command to suspend it instead:
pasuspender opensonic_launcherI have tried it with Audacity, but it will probably work with OpenSonic. The utility (pasuspender) is located (at least in openSUSE) in pasuspender-utils package. It mutes sound in all applications working with PulseAudio until the game process is exited.
