pioneer deh5900ib head unit.. custom 6x9 rear sound bar, stock soundbar went in front and a kicker L7 sub with kicker 2.450 amp..
Do not try to get good bass out of ur mid speakers. You will just waste money. I feel pretty safe saying its impossible to get good bass with the slim soundbar box.
If you want bass, get a sub.
Anyhow If you are on a budged, the first things i would recommend you do is get an aftermarket Headunit and get a sub. This way you can turn off the bass to your regular speakers so they are not sounding like crap trying to produce frequencies they cant. The sub will take care of those frequencies for you.
Later if you have left over cash, get better speakers all around.
I would also highly recommend shelf speakers or however you call them on top of the dash. Those make a big difference in voice. (Thats why i have my stock sound bar up front)
here is a pic of what i am talking about
Here is my setup