The X300 has USB capabilities. I'd forgo the CD and just run with the X300. I'm in the same boat and just gonna go aftermarket for all peices.
As for how to tell if it's a MACH 460 - If it is, there should be speakers/tweeters mounted to the doors right where the mirror housing sits. You should also have a couple of speakers and a couple of amps mounted under the rear deck.
The following link is for the MACH 460 wiring:
Mach 460 Information
About midway down the page they have a link to a zip file containing the schematics in .pdf format.
I don't have any info on the premium kit, I'm actually still looking myself.
If all else fails, call FORD. They told me what rolled off the assembly line installed on my 94.