Gotta Head Unit!!! Speaker Question!

I finally found the head unit I wanted. Its the 91-94 Buick Radio with EQ and is re-manufactured and looks like new! I am having it put in because I don't want to have to take the bracket and I'm worried about the wiring harness from the Ken-wood cassette I had in it. Long story short, to save money I thought I'd tackle the speakers myself. What brands do you recomend that are affordable. I'm planning on getting mine at pepboys so I'm sure anything there works. Also what problems will I run into when swapping the front 4X6 out and the 6X9 out. Aren't those the correct sizes?

Inside the door,the weather protector (plastic), will probably be shot. Not the end of the world if you discard it. Most speakers are plug and play. Be patient on removing the door panel,as they are notorious for being weak. If you break some christmas tree clips,Pep Boys should have them too.

Cloth on the 6X9s in the rear will likely be detached or turn to powdery in your hands. Any thin silk-like dark colored cloth will do to keep the speaker cones from filling with dust.

Take care that you make wire connections so that all speakers are in phase, not mixed with + to - and - to +. The OEM speakers should have different sized spade connections to prevent this.

Depending on the power of the magnets in the rear speakers, it may involve a bit of wrasslin to get them into place. They'll want to clamp onto any metal they get close to. Be careful with them or you'll rip a cone apart when they make the jump to the car body. It's a bit tight back there.

From experience of hearing them in friends' cars, and being a car audio nerd myself, the Infinity Kappa speakers are pretty nice.

You can get some good deals on speakers on Amazon.

It might be worth it to you to explore using an adapter in the rear to make it round like it should be.  However there are plenty of 6x9's out there to choose from as well.  even the inexpensive ones will sound much better than old used stock speakers.
Idk what size front on 93, but 96 is not a 4x6 on mine. maybe someone else can verify this for you.

The only issue with 6X9 rear speakers is the height above the mounting bracket. The stock ones are about as tall as you can go, and still get the covers back on. Some of the fronts have an ABS "bucket". Those are usually 4X6. I believe some had small round speakers as well.

There is not enough room to put a 9 inch round speaker in the rear. I have larger round speakers in the front, but the door panels were cut before I got the car. The original installer was a real butcher. I did the best to make them look professional, but it still looks a little butchered.