You'll probably get better responses if you start your own thread...
What do you have for a k member? Suspension? There are shortcomings with both factory and aftermarket when trying to work with a hemi.
XFI looks like a good system. I went megasquirt instead, given it did everything the XFI did at a lower price point (Though it required me to wire everything - definitely not plug and play).
The advantage of the factory computer is knock control. The advantage of XFI/MS3x/AEM is tunability. Pick your poison.
Don't you have a healthy big block in your car right now? I for one think your ride is pretty cool as it sits!