While Im sure its no groundbreaking technological advancement but I don't take lightly to carving away at my door assembly so I was hoping for suggestions for the cleanest way to open up 3/4" to fit them.

Pics...

http://yfrog.com/56cimg0756wj
http://yfrog.com/5mcimg0757fj

Edit: Sorry Im a dolt, they're 4x6 Openings, 6x9's would have more than enough space.

 

My personal favourite is the Dremel tool with a cut off wheel. Radiuses are a bit tricky but I can usually make them turn out OK.
I'm not sure if it is just the picture but it looks like that speaker is going to end up pointed towards the floor. If that's the case, you may want to fab something up to help point it up to help with the imaging of the speakers. Of course you'll have to check that the door panel will still go over whatevr you do.
Good luck with it!

 

he said well, depending on speaker area you might be able to make a mount that will lift speaker up and out of hole and allow you to fit what you can of the speaker to fit in hole. as phil said you have to keep checking how much space you have to lift speaker up a good way to do this is to tape a potato in the hole where your speaker is then stick a tooth pic in it slowley and carefully put w.e paneling your using ontop of it and when you take the pannel off the tooth pic will tell you where the inside of the door panel stops so you can build up to that.

 

Thanks for the suggestion. Came out better than I could've hoped..

Once the speakers screwed in there's zero reasonable movement there's like a half inch for the plastic to flex before having any chance of making noise and that's with no backbracing it and I cut the top and left the bottom 1/16th inch ridge so the speaker points up just a bit, which I think will work out perfectly.