Hi Vince. Thanks for the kind words
For the door speaker swap, the way I did it was that I unplugged the wires and used a small hacksaw to cut out the stock speakers leaving the ring that I used to mount the new speakers. The other option is to drill out the rivets and thus you can get the whole thing out. You will need to get some adaptor rings then to be able to fit the new speakers. Check out Mr_Spock build thread for pictures drilling out the rivets and my own thread for the hacksaw method. Pictures makes more sense. Both ways I think are fairly straight forward.
Regarding the amplifiers, I have the front pair and the rear pair of speakers running off the 4 channel Blaupunkt amp. Thus, I had to get another amp for the subwoofer. I could have gone with a 1 amplifier setup, which was the case until recently with the front speakers powered by the amp and the subwoofer as well in bridged mode. The rear speakers were being run off the headunit but in this case, I couldn't control front/rear fade. If I gather correctly, the outboard crossover still need to be wired to an amp to get the most out of the speakers.