Welcome to the boards. Nice Subaru.
But I must ask you to search the forums. You seem to have done enough research to know some of the basics so why stop?
I would definately recommend getting the Xenarc. New 2005 car, why get second best? And while 60w may be enough why limit yourself. Get an OPus and leave room to expand.
As for audio input, does your car have the option for an oem cd changer? If so I'd bet that there is an aux-input cable somewhere. Don't do the FM modulator.
Any more questions?