Need some help picking an adequate amp Options

[computers4kids]

Recently changed my pod speakers to the ones below and primarily just use my phone or ipod. Pretty much never listen to the radio. No amp.

I've come to the point I would like some more volume and quality sound and would like to add an amp and a sub--need your help. I don't want to cut my doors for more speakers. Hopefully a foot sub or console sub with these speakers will be adequate for me. I'm thinking of mounting a amp in my center arm rest with a little modification or behind the driver seat. I don't want to mount the amp in the trunks.

Can you help me know what size amp (RMS) I need as a minimum, number of channels, and do I need a premamp. The guy at the stereo store said I need a premamp if I want really good sound without static?? Speak slowly...I am not a stereo guy LOL (IMG:style_emoticons/default/smile.gif)

Polk Audio - 4" x 6" Plate-Mounted Speakers with Poly-Mica Composite Cones (Pair)

Handles up to 150W peak power (50W RMS)
For rich sound.
71Hz - 22kHz frequency response
For accurate sound reproduction.
3/4" silk/polymer soft dome tweeter
Delivers clear, well-defined highs.
4" x 6" poly-mica composite woofer cones and rubber surrounds
For enhanced bass response. The stiff, lightweight design delivers big sound and minimal distortion.
4 ohms impedance
Conducts power evenly to keep the speaker at an appropriate level.
91dB sensitivity
Picks up the highs and lows for faithful sound reproduction.
Balance Driver technology
For pure sound.
Pole Plate heat sink
Promotes heat dissipation for great power handling and reliability.
(IMG:http://www.914world.com/bbs2/uploads/post-4253-1257311673.jpg)