sxse wrote:size of magnets doesn't change quality, it changes power...
It changes the power handling of the speaker, but I think that's what you meant.
More importantly, it also changes the transient response of the speaker. Larger magnet = more mass that needs to move. You will also need more amplifier power to move the mass effectively. In short, the larger the driver, the slower it gets in response to musical changes.
A 6x9 in the front door isn't the best place to put that speaker. It's primarily a mid/low driver. The area behind the speaker is just as important as the size of the driver itself, and having the door panel as an enclosure for a mid/low driver would sound like a$$. Muddy midrange and terrible bass response.
You would be better off with a component setup in the front and a bass/sub-bass driver in the rear.