In my experience, and I have installed stereo systems in a LOT of cars, everytime you use an amp, it MUST be hooked up directly to the battery. Even though it is a small amp, it will still draw too much. However, you do not need to use it, your stereo is a 200 watt (50x4) preamp and will more than adequately power the speakers that you have.
If you are worried about how to run the wire for the amp from the battery, look for a rubber nipple on your firewall with shrouded wires coming from it, carefully cut a 1/2 inch slit in it, push a 4 or 6 guage power wire through it and it will come in under your dash.
Unless you plan on doing a lot more with your ICE, just leave the amp off for now, it'll save you a lot of headaches from trying to tune it to sound good. Pioneer makes very decent quality head units and the internal EQs are good enough.
If this helps you at all, I'm happy. If not, feel free to disregard everything I just said.
Chuck