Honestly, I have the upgraded sound system in my box and it sounds just fine. I got it that way when I bought it so it was money saved by the time the final deal was worked out.
I do plan on replacing the Bazooka tube but only because I want that space regained. I'm weighing my options and I like the under seat idea for the bass speakers. One bass speaker will do me just fine. I like to feel my music but I don't want to advertise.
What I'd really like to do is change the actual head unit to something more iPod friendly.
So I guess I'm the only one here that gives the stock upgraded sound system a thumbs up. Now to totally contradict myself in a way. If you do not have this option yet and are thinking about getting it in a new xB... DON'T! Save your money and space in the back. Get an after market! You will most likely be happier with the extra money and space saved.
In our camo green XB we are running the Stock head unit. The front speakers we replaced with top of the line Boston Acoustic componets with an amp. Then two 12" Kickers squares with another amp for that. Anyone locally can vouch that it sounds nice.