Replacing 8 speaker system, choices for amps Options

[RocketScott]

So I have an 8 speaker system and I'm slowly replacing parts of it. I just put in an Alpine CDE-9845 head unit. I replaced the 8" door woofers with some Alpine 6180 subwoofers. I also have some Kicker KS60 coaxal speakers in my truck that I think I'll put in the back seat. I yanked out the two factory amps and am running everything off the HU except the subs which I now need an amp for. I'd eventually like to replace the midrange and tweeters in the doors with a component system but I haven't seen any that will fit. The smallest I've seen is around 5" IIRC. So do I get a mono amp to just run the subs for now and get another amp later to run the rest of the speakers when I upgrade or do I get one big amp now that will run it all? The head unit has two sets of RCA outs, one for the front and one for the rear/subs

[RocketScott]

OK, so I figured it out on my own. I ended up getting this amp:

http://www.circuitcity.com/ssm/Kicker-2-Ch...roductDetail.do

I have it just powering the subs and everything else is off the head unit. Later on I can get another amp to power the rest. I got a Metra wiring harness from Autozone to connect everything except the amp and subs.

This amp fits under the drivers seat perfectly. It has removable end caps to make it smaller but is exactly the right size with them on.