I've done some snooping around, and I couldn't get the grilles of the top of the rear decklid either.. I thinking that there must be a neat trick to it.
I measured the DC resistance of all the speakers that I could get to. The 2" Dome tweeters in the A pillar about 3.5 Ohms, so probably 4 Ohm Impedance tweeters. The 2" size is going to get me though.
The 6 x 9's in the back measure at about 1.6 to 2 Ohms, so I'd bet that they're 2 Ohm impedance. Not too common, as most 6 x 9's that I've looked at are 4 Ohms.
I've already ordered a set of Infinity 10.5 series 1" Tweeters to complement the front "Twidlers", that should bring out the life like sound dramatically, but I'm still hesitant about getting a set of Infinity 3-way 6 x 9's since they're 4 Ohms.. Probably not that big of a deal, but I'm looking for more sound, as well as better. I may end up replacing the Bose amp in the trunk at some point, since it's kind of lame.
I'm thinking that I might be able to dig up a sweet Mark Levinson 12 channel amp, and see if I can rig up a harness adapter with the right pin-outs. The 9" door subs are the only problem. It's not going to be easy to replace those without putting a 10" sub in the trunk.. Even though I'll probably put a sub in the trunk anyways..