I've the Logic 7 in my car and am quite impressed with it, I suppose it all depends what you've been used to. My last car (E46) only had pretty much standard speaker setup, so going to L7 was a great upgrade.
I'm pretty sure trying to upgrade to an Individual speaker set up would cost a fortune, that is if its posible. You would need to get all the parts from BMW, and they will rape your wallet for them. It would be more cost effective taking the car a to a professional install place and letting them give you a quote on an aftermarket setup.

I have no personal experience with them yet, but some of their systems look pretty good. All plug and play.

http://www.bavariansoundwerks.com/

Each to their own tastes poot1873. I find the sound does not have enough top end - almost like the sound is muffled. I have a set of expensive in-ear buds which are my benchmark and the BM set is not comparable. When looking around, I came across a good comparison between the pre and post LCI Logic 7 and there is a definate sound quality reduction. It is possible that BMW chose to rectify that later after the LCI came out hence yours sounding ok? who knows...
I have also looked at the link, thanks locomtiveBart, and am considering them as an alternative. I like that they are also developing an amp also which (possibly) addresses some of my concerns with the installation, but will have to see.

I really would like to try this retrofit, but do not want to buy parts only to find that they do not work as expected - i can get them cheaper than BMW but not enough to 'suck it and see'!!!

Bruce, can you give some more info about what those other differences are? I have located the amp, speakers and crossovers from RealOEM and cannot locate anything else which may be part of this setup?

OEM always sucks, go aftermarket. Check out these threads from Technic

http://www.e90post.com/forums/showthread.php?t=508584

http://www.e90post.com/forums/showthread.php?t=508793

as you can see you can overhaul your entire system without going broke.