I think acoustically 6x9's just don't belong in the front. They would be too full bodied. Bass is obviously non-directional, but it's my belief that up front you're better having speakers with more natural treble and a little mid-range than just bass/treble and midrange.
I could be talking crap, if I am I'm sorry that's just what I've found, in and out of cars (guitarist as well).