Replying to Car stereo question...

Ok, so right now, i have

2 eclipse tweeters
2 6.5" eclipse door speakers
an eclipse CD deck
2 eclipse 6x9's
one 12" alumapro BP 12 subwoofer
and a 5 channel 1560W Memphis Belle amp.

Everything runs fine right now, but since there are no door speakers in the back seats, and the 6x9s are all the way in the back (4runner), i wanted to put in a couple of 6.5" speakers in the back seat.

I don't have enough channels on my amp. 4+sub channel, is there a way to bridge, so that i can power these using the same amp? If not, should i get a seperate subwoofer amp to power my sub, and run the back door speakers off the fifth channel? Or should i get a seperate amp just to run the back door speakers (seems kind of futile).

I'm thinking of a seperate sub amp, but here's my question, what kind would you recommend? where can i get it at a good deal? and HOW MANY WATTS should i get to fully power my Alumapro, i dont want it to be underpowered!!!!!!!!

thanks!