Slightly OT - Impedance matching device

[swinginguitar]

Not necessarily stompbox, but....

I run the headphone out from my MP3 player to line in on my car - and get the usual treble loss, volume loss etc.

Does anyone know of a way I could put together a device to match these? Passive would be nice, but perhaps a low current active device would be OK....

[CynicalMan]

MP3 player outputs have low output impedance because they have to drive headphones. The problem is probably that the mp3 player's output is lower than the car amp was built for. A pre-amp might help.