Regarding sound, I think there might be another solution. Instead of redirecting the mecanical sounds from unity (which seems not implemented by now), I will take a look at VPM source. Thus, if possible, I'll add first a function to control sound volume directly (common to ALL roms) and then, maybe another function to use a second device. So you will have to switch outputs but that should do the job.
I think there was a bit too much confusion with this.
What is implemented in VP is pretty stupid: The user can simply select a soundcard from the ones installed on his/her system. That's it.
This way all sounds that VP generates (typically all the mechanical and ball rolling, etc) can come from a different soundcard then from the one VPM uses.
Very simple 
I've modded my copy of VP to allow me to target sounds to different sound devices. This way I can have the mechanical sounds coming from the playfield TV's speakers, and the music and other "backglass" sounds coming from the backglass speakers in my cab. Some tables like LOTR aren't using Vpinmame audio for performance reasons, or are recreations (AC/DC), so just relying on VPinMame to send its sound somewhere else isn't quite sufficient. (I will share this mod when VP 9.2 is released).
Since this is a new project, it would be nice to build in proper support for different sound "types" from the get-go. Then it would be easier to direct sounds where we want them, or turn them off if the cab has mechanical toys to do it instead in a standard manner, instead of having to hack tables individually depending on how the cab is configured.
Edited by DJRobX, 17 December 2013 - 09:46 PM.