Does your 08 Have NavTraffic? If it does than you can not add it, because the Satellite is built into the navigation system. There is no input slot to plug anything in. If you don't have NavTraffic, you can add it and have both XM & Ipod, you will have to undock the Ipod to revert back to satellite radio.
I came across a thread were you talked about NavTraffic. Don’t think it’s an option for the Titan. The 08 Navigation System manual doesn’t say anything about NavTraffic..The manual covers Titan, Quest, Maxima, and 350z only.