Jim Weir: help to add car radio to aviation audio panel music input

Jim,

I've read your columns regarding aircraft electronics for years and I
just can't seem to get an answer for a problem I have. I'm trying to
connect a Alpine AM/FM/CD player in my plane to the music input of my
audio panel (a GMA340) The problem is that I can't hear the music
because the volume is so low. I believe it has something to do with
the input and output level of the two devices, but not being an
electronics guru I don't know how I can make them work together. Do you
have any suggestions? The output of the radio (pre-amplified) is 4V /
10K ohms max voltage and the audio panel music input is 510 ohm
impedance and 500 mV RMS for full output typical, 1V AC RMS MAX (3V
peak to peak).

I'd be happy to supply more info is required. This is probably a
simple question, but I'm stumped!

Regards,
Brian DeFord