I think it is safe to assume that some one else out there has installed an Empeg in a VW with the Monsoon setup. Check the install forum for starters. An FM modulator is probably not your only option.

Also take a gander over to VW Vortex car audio forum and see if they can help you out. I do see a few posts mentioning the Empeg & RioCar.

Not too sure if this helps as it might only work with the non-Monsoon system.

So just keep looking.