Stage 1 of the audio system is now done: I fitted the Focal speaker replacement kit IS165TOY. I've followed many people here so I'll just say that you really must have a plastic pry tool to pull the door panels off. I also put a piece of 300 x 200mm approximately acoustic foam behind each door speaker, behind the window rails so that they won't interfere with the opening windows. The tweeters were relatively easy to do, but again that pry tool is essential if you don't want to damage the plastic interface.
I also suffered the faulted windows after reassembly but that's easy to fix: press and hold both buttons in the down position for 15s, then pull and hold both up for another 15s. This resets the stored position memory and stops the window button lights from flashing.
The sound is way better than before, it actually communicates the music rather than the tinny pathetic noises it made before. Highly recommended speaker kit.