The empeg tuner is controlled over a simple 3-wire RS232-style serial port. Look into the kernel source file serial_sa1100.c for more info. With the Hijack kernel source tree, you'll see the CONFIG_HIJACK_TUNER code in there to "emulate" a tuner.

That oughta be a good starting point.

The tuner audio is transmitted to empeg over separate analog audio lines.