6 x 9's

[sharma]

Hi,
I have a set of components up front in my Audi a3 and a sub in the boot. I have 2 amps to run this and it sounds good. However i would like some treble comming from the back of the car too. I know it would make much difference for me sitting in the front, however it will still make it sound fuller and people sitting in the back can hear more treble rather than just bass.
I have a good set of 6 x 9's and am thinking about buying a stealth shelf and putting them in. There are mixed views on this. But my amp will be set to high pass so that little bass and more treble goes though to the 6 x 9's. What do you guys think about this? (Not sure if its a myth but i have heard the 6 x 9's fight the sub for air).