My Ipod is way too quiet in my car?

I bought a 160gb ipod classic. Took me forever to put all my music on there. I saved it with the volume limit on itunes all the way up. Ive adjusted everything i can find on the Ipod itself to increase the volume. I use a AUX connection which goes straight to the stereo. Still with the volume on the ipod at the max and the volume on the stereo on max its waaay too quiet. If im listening to the stereo or a cd i only have to turn the volume half way up to get the volume im looking for. What can I do??? Its so bad if i roll down the windows its not even loud enough to make out what song is on! There has to be a better way! HELP!!!