I can see that there are only 2 rca outputs that are mono on the G4. I have a system in my car where i have the front speakers and sub connected to a amplifier and the rear speakers are connected to the headunit. If you buy a usb soundcard to deliver sound to the front speakers and sub via the amp, will there be signal on the rear output on the G4 so I can use that right on the rear speakers? And will the fade (volume) between front and rear work?