I searched and searched to figure out how to use my 8 pin DIN connection on my Clarion HU for AUX sound in. After ordering the service manual and confering with Electroken on the Xterra Owner's Club message board, I now have an AUX input for my HU.
The HU in my 2000 XE Xterra is a Clarion CD AM/FM unit. It's model PN-22181. Here is a picture of the pinout for the DIN connector:
Hook your left and right audio inputs as shown and provide #1 with + 12 volts and viola music through the Head Unit. I hope this helps someone and thanks to ElectroKen for figuring it out for me.