Thanks. I've tried two of the "broadcast" units to hook my player up in
the car, and I've not been overwhelmed.

It's been my experience that all FM modulators are just truly awful. Barely
a step above are the adapters that plug into the cassette player. The bottom
line is that to be listenable, the audio signal needs to be fed to the
amplifier at line level with no previous conversion, just as your components
are at home. That only leaves two options if your current head unit does
not have a line level auxiliary input. 1). Replace the head unit with one
that does have an aux input (most newer ones do now, because of the iPod
phenomenon. 2). Have your head unit or, as in my case, the path between
the head unit and the power amps altered to allow for a line level aux
input.