The "Rear In" connection is the audio feed from the TV. If you have a factory installed DVD, this might be the setting you are looking for.
I'm not sure how yours is wired, but I would think that the DVD would be wired directly to the radio. If you are adding a DVD I think I saw some unused connectors that were taped up.
There is a submenu selection for the mic in. I don't remember where it is. The Sony owners manual is very good as it covers everything. There might also be an installation sheet(s) that show how to wire additional components. I'm at work, but I'll look when I get home.
Have you tried connecting the DVD to the Aux connection?