I have the same problem. There is a workaround that doesn't require reinstalling the drivers. Every time you reboot, go into the SupremeFX manager and recombine the front and back interfaces and check the box to mute the rear sound when something is plugged into the front. Hit OK on the screen, then go back in and change it back to have separate interfaces.
Hopefully whoever is doing the driver development can figure out why the settings aren't persisting through reboot. I went ahead and ordered a little USB sound card to plug in the front of the case for now so I won't have to hassle with it (cheap ones are 5-10 bucks). But I'd much rather use the case ports and tie up one less USB.