It's great to have the info on different setup options so everyone can see what is possible to get what suits you best. I always think sound is a very personal thing and at the moment I settle for something that isn't where I would like it to be but is better than the HK setup from BMW.
There used to be a company, name escapes me now, that built door cards with the original leather etc. that housed 4 speakers i think. I seem to remember seeing a pic of a Zed with this setup but never heard it running but was something i was considering at one stage. Currently my sub sits upward between the hoops which, while not ideal, sounds so much better than the rattling embarrassment provided by the HK option.
Plenty of food for thought here and maybe we could start an audio wiki section at some stage of how to achieve different sound setups to suit different listening styles? I'm sure everyone would appreciate different stages of upgrades to get an idea of costs to improve a specific area or go the whole hog and replace everything. we could maybe keep in mind the type of music the person listens to as someone listening to classical music is most probably going to want something quite different to someone wanting the sub bass from a dubstep track and then maybe a mix between the two?
I'm no sound expert, as you can tell, but that's where the community experience and knowledge comes in to get ideas, now where is my lottery ticket!