Ok here we go.
Door speakers are 16cm so you can fit 6,5" or 7" ones. There is a high probability that you will need to change factory adapters to which speakers are mounted and build yourself ones from mdf. Not sure why you would need any adapters for the speaker wires when you can simply cut them in the door, use connectors and connect them. There are many better speakers than alpine (not counting F1's obviously) or jbl. As an example: focal, rainbow, morel, hertz, hybrid audio, brax. If you really want to change speakers you will have to go for component ones and stay away from coaxials. To be honest I wouldn't install any rear speakers and just focus on good front and sub but I understand that a lot of people do like some sound from behind for some reason.
Problem is that changing speakers on their own will not give you better quality. In fact it might be even worse.
If you have non bose system, your rear speakers and subwoofer are run through amplifier but front ones are from cd player.
Now, the problem is that if you stick better speakers in the door, they will be underpowered for most of the time because they are higher power than audi system. If they are underpowered you will lack control in both low and high.
The only way to "make" the system sound better is to use after-market amplifier. For front, rear & sub you would need 5-6 channels in total, so either:
- 2channel + 2 channel + 1(2) channel amps (3 amplifiers)
- 4 channel + 1(2) channel amps (2 amplifiers)
- 5(or 6) channel one (1 amplifier).
That's obviously if you don't want to go active because this would change.
Another problem with keeping RNSe is that there is no RCA output so you would need to use some additional processor like Audison BitTen, BitOne, JL Cleansweep or Alpine one, which are not cheap at all. You would need to get all new wiring (power, rca, speaker) to make it work. Also if you stick cash in front component speakers it would be rude not to sound deaden at least the door and boot.
I'm not sure what size the subwoofer is but it is tiny and I wouldn't bother to fit another one in the same place.
Any SQ 10" sub in a closed box will give you better results than sticking to factory place and will not take much space.
Overall, if you want to go SQ in B7, either go big or don't go at all.
It just won't be worth to buy speakers on their own because you will be disappointed.
You could probably get a nice system just under £2k if you bought front, sub, amp, wiring, deadening and processor and if you fitted it yourself. If you want to go really big... it might cost you more than B7. And that's why I drive with a standard system after spending over £6k in my Mondeo. I do miss it badly though...
