I've done a little research on the subject, and I want to implement rear fill in the form of difference channels delayed past the haas effect. I have the drivers and processing necessary, but my one thing I'm really stumped on is creating the channel in general.
I know that if you use Y-Cables, you'll just end up having a mono L+R channel, so that's not going to work.
My thoughts are to use the speaker outputs of my DEH-80PRS, and take the pairs (L+ and R+) (L- and R-) to plug into the processor's speaker input pairs, (L+ and L-) (R+ and R-) respectively. My concerns are that the output of the head unit is not a balanced input, and the L+ and R+ are the only data sending wires, where the L- and R- are ground, and also that the head unit may not appreciate being wired in this manner.
My other option I thought of was finding an RCA to Balanced transformer, and plugging in XLR cables at one end, and splicing the pairs needed into RCA connectors, grounding the opposite end at the chassis of the processor.
Besides that, I'm stumped, and I don't know if either of my ideas will work. Any incite is greatly appreciated.