I can answer this one easy. I used to work at Audio Express for a number of years installing stuff and I ran my own audio company that did custom stuff. And yes, my championship sound vehicle from MTX makes me kinda knowlegable.
The sound bar is fine if you get speakers that are meant to be installed in an open air environment. Most speakers offered at most stores require a bit of baffling to produce the advertised sound. Pyramid used to make a baffle attachment just for the XJ sound bar. There are a few cheap tricks you can do to 'adjust' the output of the speakers you without resorting to electronic means (screwing with the EQ or other annoying settings)
The material that xjjeepthing showed you is great stuff for the speakers in the $20 to $80 price range (I used price range since that groups alot of the same speaker offerings to an area of sameness in sound reproduction)
My old favorite, which works wonders if done right (hard to mess up) is to 'seal' the speaker. Take the speaker cage and find a 2 liter plastic bottle. cut the bottle so as to use the bottom end as a baffle and duct tape that sucker on there making sure that you totally enclose the rear of the speaker air tight (as much as possible) cut a 1/2" hole in the rear of your new baffle. Viola! you now have a new 'tuned' speaker, which will produce a more fuller sound. If you made it right it wil barely fit inside your sound bar (cut into ceiling if you like to get more room).
I used to do all kinds of stuff like that for my buddies in highschool who could not afford the serious stuff but wanted better sound. Messing with the EQ's in on your deck will only frustrate you, since the music that is pumped off a CD or the radio is designed for your system to be in a flat state (mid level for each of the ranges) since that is what the majority of consumers have there system set to (default settings).