You pretty much have worked it out.

Yes, the Tuner interface is very low-level and the tuner module does little else than accept I2C commands to read and write certain registers on the Tuner module in the tuner.

The 'smarts' are all on the Empeg itself, either in the DSP (where the RDS signal is processed), or in the kernel and/or player software (for the tuning, user interface etc).