Hi Guys,
Standard Speaker set up non HK:
Front footwell = 5.25" component speaker
Door = 1' tweeter
Rear Behind Seat = 3" component Speaker (cannot fit larger than 3" in a pre face lift, will need to cut plastic, so might as well fit 5.25". you can fit 4" in a post face lift, but need a slim height 4", this will fit under standard grille.
HK system as above plus:
Door = 1" mid range
Subwoofer = 2 x 4" woofer (1 inverse mounted), only way to make sub work in this tiny volume area.
no doubt extra amps in as well
Note the real issue with upgrading speakers on either the non HK or the HK system is that the amplifiers used are underpowered and highly stressed so wont take big RMS speakers, but improvements can be made by swapping all the component parts out (speakers) and changing the HU. Alternately replace all component speakers, run new wires and fit bespoke Amps and a nice high powered slim sub.
Hope this helps