I did this for a while with an EQ and a 1/8th inch jack-to-RCA adapter. Adjusted volume with iPod. Worked great, wanted a headunit though. Just be careful with the volume, figure out where it gets distorted at and keep it a couple notches below that. If you have a compatible iPod I suggest checking out Rockbox. It has a lot of advanced EQ and audio settings that make it just like, if not better than most headunits.