I have just fitted 4 5.25" Orion CO500 speakers to my X300. the old speakers I removed were 3 x 4" American HiFi TX4002 and a 6" speaker of a unknown brand from the left rear door.
I found removing the door trims very easy compared with some other cars I have done and the speakers fitted perfectly the holes for the screws didn't line up with anything there which was blessing as I had some self drilling cabinet making screws that hold the speakers nice and tight in the door trims. I soldered the speaker wires to the connection on the speakers but cut the speaker wires closer to the wiring loom and fitted screw block type wire connecters to join the wire so that it makes it easier to disconnect the speakers if I nead to remove the door trims again.

These Orion speakers sound really good I can hear detail in the music I couldn't hear with the others and they have a nice sound I am no expert with speakers and sound but I am happy with them and the installation I did.

Cheers Derek
95 4L Jaguar Sovereign