2 Speakers in the rear what for. I don't sit in rear. I am always in front. So no worry if the rear passengers(if there are any) cannot enjoy music.
I thought 4 speakers in front because then I have surround sound in front. Its really nice to listen to music from 4 speakers(4 proper speakers) Ask B&T he has done so in a 8K install
Ideally I think the sub should be in front. I guess lack of space is the problem. That way I can enjoy music in front.
EDIT: How about a JBL 4 inch 2 way thingy for Dash(2500 approx) and JBL 6 inch loudspeaker for around 2700 in the doors. Or 5inch 2 way for the doors.
I can also go for 6 inch 3-way or 4 way speaker instead of 4 speakers in front.
The criteria is front soundstage.