"Optional" means that there is no tuner inside the new unit. There is a tuner bus, with a flying lead & connector, in the mk2 wiring harness.

The tuner module isn't another head unit. It's a small box - around 4"x2"x2" - with no buttons, switches, or lights on it, just an antenna connector and a lead which connects to the wiring harness. The tuner is totally controlled by the empeg, which autodetects its presence. You just have to hide this little box somewhere behind the dash.

Hugo