Originally Posted by
anwaypasible 
there's usually only two reasons for those kick panels:
1. because it made the distance from one speaker more equal to the distance of the other speaker (but this was before distance delays on the head unit)
2. because of the reflections that would accumulate .. sometimes it would be better to use the roof and rear window to accumulate soundwaves, while other times it was better to use the door location.
number 2 is inolved with the total response inside the cabin.
it could be frequency response
it could be phase response
it could be the timing of the reflections being more or less the same throughout the frequency range.
i am the type to get in there and do it and see for myself, instead of having computer processing software to answer those questions for me.
(seems like the only two options doing it yourself, and other than that a person to simply know the answer .. but i dont know the answer)
it might be wise to get a plate speaker.
but it might also be wise to keep the 4x6 shape.
see..
in the rear window of many cars, the window is angled.. and sometimes there is a bend to the window seperate of the angle.
and because the rear deck sits below the window, there is like a pocket of space there.
the wide part of the 6x9 (the 9 inch part) can help fill up the air of that pocket with a more wide soundwave.
i look at it like this..
two round speakers might leave some empty gaps in that pocket of air.
while the oval speakers could fill in the pocket with less empty gaps.
and to the listener, that means the sound coming from the pocket of space is more like an ocean tide compared to getting squirted with a hose.
either way is getting wet, but if you could get the soundstage to blend together like one big chunk of audio .. it sounds better than listening to the round cone bounce the soundwaves around in the empty spaces like a slinky going down the stairs mixed with a rubber bouncy ball from the quarter machine.
if the 4x6 was in the door..
does the wide part simply go straight into the driver or passenger leg?
or does it have a better purpose like shaping the soundwave to miss the dashboard?
but the dashboard is only one half of the output pattern.
the other half is towards the listening position.
see for the rear window example.. the sound is basically coming from that general area.
it means the sound could come from the window just as much as it could the speaker cone .. but the cone isnt pointed at my ears, so that really says the sound will come more from the window .. even if it is 51% compared to 49% .. the 1% is more.
for front speakers in the door.. the circle pattern could really prove helpful when thinking about the listening position.
and the only way to think of it for anything better is to also think about the shape of the vehicle those soundwaves are bumping into.
(like the flat rear window and the roof.. as well as the angle of those shapes to the speaker)
because maybe the oval speaker slides across the L shape .. maybe the circle shape will hit the L and slide less and then just cause a bunch of soundwaves to fight in as they are trapped in the corner by the window seal (or where the roof meets the window body panel).
if you think about which shape you need first.. you wont be wasting any money when you get some speakers.
as for which speakers, it gets harder and harder to hear them personally to give an experienced answer.
and it really isnt fair to just use the name brand of the speaker as a quality answer, because the typical car audio companies are not always selling the same quality of speaker clarity.
it is true still..
sometimes one brand name will always show some improvement over another one when you simply drop in the speaker and start up some audio.
and people look at one name brand like a 'low quality oem replacement' ..while the other company always tries to aim for 'mid-grade premium oem replacement'
sometimes the only premium is the number of extra watts the speaker will take in (and how much louder it is compared to the oem system).
End of the day, it's whether you are happy with your purchase. And I believe you are. So who cares where the thing is made?
