2 Subs, Configuration?

Still a newbie to these forums but this is the best place I've found for anything I've needed so far :)

Anyways: 

1998 Monte Carlo

Right now I have the amp bridged from 4 channels to 2, each of those channels driving a sub.  Since I installed my HU (Pioneer DEH45-DH) the stock 6x9s in the back have given up the ghost and I have next to no midrange except coming from the door speakers (recently replaced, sounds fine).  I've ordered new 6x9s to replace the stock ones, but I was thinking of unbridging the amp, using two channels to power the 6x9s and two to power the subs.

Which of the following ways would give me the most volume/power to the subs:

Any off the cuff help is appreciated.  Everything except the HU is Pyle, I'll give the model numbers if you really want (amp is stable at the three conditions above).  Pretty much everything is starter gear because I want to learn as much as I can, do it all myself, and for now not risk blowing out anything that'll make me cry.

Well I don't want to see you cry.....I if you are looking for the most power to the subs then from my calc. you have it set up already for this. A question for ya, what do you mean an open box? ported?  My one suggestion would be to get a a sub amp and use the 4 channel to power the rest of your speakers, you'll like it and so will your new speakers.

By open box I mean the subs mount to the front, covered by a set of open grills to allow them to extend safely.  Again, it's beginner gear, I want to start with the basics then work up to the good stuff.

I am considering buying a 2nd amp and re-wiring (right now I've got 4 gauge power wire to my one amp, no distro block) but I want to see what I can get out of the system once I install the speakers without adding anything additional.  Really just wondering what would be the best option wiring the most power to the subs assuming I'm already using 2 of the 4 channels to power the new 6x9s.  I guess an option I didn't list is to leave the amp/subs how they are and just use the HU for the 6x9s (Probably wire up like this first since I have a spare set of GM speaker harness.

Thanks for the quick replies Xtremej! That's why I love the forums here.  Any other suggestions are of course welcome but looks like I'll try hooking the 6x9s right into the factory wiring before I do anything with amp configurations.

(Might not last long though, between my wife and I we listen to a wide array of music, so big thump isn't everything but it has to be there)