Volvo factory navigation installation help

I really need somebodies technical help on installing a used (2005) navigation system into my wife's XC90. I'm getting alot of conflicting dealer part info. Let me say first off, that the parts I bought have the same factory part numbers that the dealer said are shown for her 2004 XC90. It appears most dealers do not want to install a used system. I've bought about $300 worth of the additional parts that are required. I do have the install manual, and the following parts: The Control unit, The display unit, the fiber optic wiring harness, the hard cable wiring harness, the remote control, the navigation grill & the latest nav-tech discs. My dealer is gun shy on even trying this install. Another has warranty concerns and just won't do it. I contacted a very knowledgable dealer who has been selling these kits on-line and he says that my contol unit is not compatible with the XC90. I have a technical background, but I'm really stuck as to what to do next! Please help if you can. Thanks, Jake3131