Run Crystals in the back or not?

I just got in my new SSCS 6's today and want to install them this weekend, but i havent chosen an amp for them. Im debating on wether or not running another set of crystals in the back and running a 4 channel amp would be overkill. I really like the sense of music coming from all around me, and did a little testing with the STOCKERS, shifting the stage from the front to the back of the car...keep in mind my car is a pretty small hatch and i will be running a SI MAG very soon. I did not like it when only the music was coming from in front of me...

How many of you guys have experience running 2 sets of components in your car and enjoy it? I dont want to risk my car sounding cluttered or crappy, but i do want to decide what to do soon so i can buy this amp..

Its either gonna be this for the 2 channel option...

http://massiveaudio.com/lowband/products/amplifiers/proAB/p200-2.html

Or this for the 4 channel...

http://massiveaudio.com/lowband/products/amplifiers/proAB/p400-4.html