That's what I was thinking too, 4 ohms should be easier on the amp, but wouldn't play as loud (easily fixed with fader controls, though). Not sure if Crutchfield's info is right, though. It's an 8 speaker system
A 6.5" in the lower front corner of each door and a tweeter above it. Something is strange about the rear speakers, though. The mids don't put out anywhere near as much high frequency as the front mids. I'm suspecting they're actually set up to be mid-basses. Whatever Dodge and Infinity did, it works, though. Sounds great for a factory system. Hell, it sounds better than quite a few aftermarket systems I've heard.
Ahh, I see where the 6 speaker thing is. There's no option for Infinity in their system for 2000. Mine's an '01, which seems to have the right info.
After digging around a bit, I wonder if 5.5"s in the front doors would work better. Should give more of the high frequencies, then some 6.5"s in the back could handle the lower stuff. I'm not going to bother with a sub, unless I can stuff it under the plastic on the right rear corner. There looks to be some room there, but I haven't taken it apart to see what's in the spot.