Saab Audio System-AS3 vs AS2 and new Speakers or Factory?

I've seen a lot of ways people have done things, but on a whole, it seems like aftermarket head units do not look stealth and clean like the Saab OEM one does. So I am likely keeping the OEM one unless someone can tell me otherwise about any aftermarket one looking and sounding better.

Questions:

1) I am parting out an 00 Aero w/AS3 system. My other Aero is an AS2 car. Is there a lot of legwork getting the AS3 electronics/wiring into the AS2 car and is it even worth doing so?

2) Do people like aftermarket speakers better than the OEM H/K speakers?

3) Does anyone know the impedance and the frequency range that the speakers in the car play? I am primarily interested in the front door, front tweeter and possibly rear shelf woofers. I won't be using the rear door speakers.

Thanks!