i tried doing a search to find out if it is possible to upgrade to the THX system, but i couldnt find any, it would not recognize 3 letters, does anyone know if this is possible, thanks

This has been talked about before and it was deemed far too expensive and complicated to justify. It is much better to just get an aftermarket system that, while not being stock, will perform much better. Several people on this site have installed DVD/Nav systems in their LS's and have been quite happy with them. There is also a kit to make your steering wheel controls work with an aftermarket system. So no worries there.

Yep, that's been the consensus. Doing it right means buying new wiring harnesses (including, IIRC, the main body harness), running shielded cable hither and yon, and generally doing at least as much work and spending at least as much money as it would take to install a nicer aftermarket system. So, it can be done, but really only to prove that it can be done; it just doesn't make sense to do it.

FYI: If you are trying to search for something 3 letters you can add an asterik at the end. ie "THX*"

Read through this:

http://www.lincolnvscadillac.com/showthread.php?t=18030