Sorry, I made a mistake in my earlier post. The tweets are actually 4ohm, it's the mid-bass that are 2ohm (
http://www.zpost.com/forums/showthread.php?t=675918)
Yes, those are the CDT mid's that I used. They fit fine in the doors you/installer will just have to make an adapter to hold them to the doors.
Regarding the mid's behind the seats, I just don't run them. Because of their location the seats block most of their sound, only having mid-frequencies coming from the rear is just plain strange and figuring out how to drive and control them is just another headache (never mind if you wanted to swap something in there, since it's a bear to get at them).
Given that the stock mid-bass are 2ohm if you want to use the amp in the HU you'll
have to go with aftermarket drivers. Since this sounds how you want to go, then "yes" it seems like you could use that HU to drive the aftermarket fronts.
This leaves the challenge of where to get signal for the sub from. Ask your installer. One solution I can think of is to use a passive crossover for the tweets/mids run off the HU amp, the mid-bass run off the HU amp, then feed the amp for the sub off the HU sub signal. You'll just have to make sure the sub amp you plan to use can take a line-level signal in (or use a Line-Out converter)