Q: "See the Preferences | Audio Options dialog" - but wont both effects and rom still use the "sounds" preference? Or are you saying music is perhaps the rom sounds and everything else is just "sounds"?
The dialog is pretty confusing - it uses inconsistent terminology and is laid out with the items on the left in the opposite order from the items on the right. Here's what it all means:
On the left side, the top set of "Music" controls - "Play Music" / "Music Volume" - is referring to the ROM audio. "Play Sounds" / "Sound Volume" is referring to the table sound effects generated by the Visual Basic script.
On the right side, the top list - "Output Sound Device" - is referring to the table sound effects from the VB script. The bottom set - "Backglass Sound Device" - is referring to the VPinMAME/ROM audio.
So "Backglass" == "Music" == ROM audio, and "Output Sound" == "Sounds" == table effects.
If you want to separate the audio, you just have to select different sound cards for the "Output Sound Device" and the "Backglass Sound Device". You'll of course have to physically install two sound cards before you can select different ones. Once you do, select the card that's hooked up to the backglass speakers for "Backglass Sound Device" and select the one that's wired to the cabinet speakers for "Output Sound Device".
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There's one more bit of trivia to this that you might want to know about. You can choose to route *individual* table sound effects in individual tables to the backglass speakers. This is intended for old ROM-less EM machines that have chimes for scoring. If a table doesn't have ROMs, VPinMAME isn't involved, so *everything* that table plays will come from the cabinet speakers. That sounds weird for the scoring chimes. Fortunately you can fix this for individual sound effects. Open the table in the VP editor and go to the Table | Sound Manager... dialog. Find a sound effect that you want to route to the backbox speakers. Click on its name in the list, then click the "To BG Out" button ("BG" == backglass). Repeat for each appropriate sound. Click OK. Those sounds will now come from the backglass.