Just went and had a chat with these guys, a chap called Gary. They seem very professional and thorough, appreciate the need for quality and found the shoddy bits of my current system very quickly. They have a solution for my lack of front-rear fader that's causing all the sound to come from behind me and will also re-fit the door speakers with plenty of sound-proofing to improve the quality of the output.
I'm due to drop the car off in a couple of weeks as I'm too busy at the moment...install price includes a loan car, but not expecting a Maser unfortunately... : )
Thanks for the pointer, Noor. I'll update you when I've had the work done.