Oh, well in that case, if the level wire goes all the way to the empeg, then it must connect to the saa7705h DSP chip. The datasheet for that will describe where it goes from there, and it undoubtedly is readable from a DSP register.

EDIT: from perusing the datasheet, it seems that the FM level info gets rolled into a noise measurement that can be incorporated into the RDS data, which is read out and processed by the player app.

-ml