Can you hear me now?

I have decided that along with a BL savage, i want to re-do my sound system. I have had the Same Costco radio for 4 years now. what attracted me to it in the first place was the fact that it came with a 4" sub. it has been so long i don't remember the exact specs.... i was thinking of running a 400watt amp, and sub. Can get a setup like that for $150 or so. thinking of running stock speakers. I don't know much about sound...systems, so i do need some help. My current sub and head unit are connected by a cable with a circle connector (with prongs inside) on each end. not sure if this is universal, most i've seen just have a copper wire that is clamped to get a connection... I do not have much to spend. just looking to give it a facelift, and maybe shake the house while i'm at it. looking for you're thoughts on equipement. Takedown reccomended parts express. They seem to have good prices on car audio equipment. I was also shocked to find out that subs actually do produce a voice, not just boom boom. I unpluged both my speakers, and turned up the treble and the base down. I'll be damned, i could hear the guys voice. I'm sure this would be greatly magnified with a higher power sub, and i am going to be running 1-2 stock speakers. What do you think?