Help me out!

Here's the deal. I bought a cheap DVD player for my truck, and it works really nice and all, however on the player itself, there is no volume control or anything, it all has to be done by remote. i was wondering what i would need to buy to be able to use the DVD player to play movies and MP3's, but be able to use my regular head unit to turn up volume. the problem is my head unit doesn't have an audio input, so it's not just that easy. would an RF modulator work for me? help me out guys!!!!