I've now completed the fitment of the new speakers. The door pockets need to be removed, they are held onto the door card with several screws. The speaker grills have four threaded shafts that fit from the front through the door pocket and speaker lugs, with a nut holding things together.
The below picture shows a fitted speaker. They aren't as discreet as the standard items which have a black mesh covering so that the driver is unseen. For a more original looking speaker upgrade I'd go for a black speaker, though I don't think the new speakers will be especially noticeable once the door cards are fitted. That said, I do like the silver, it looks purposeful.