I have been doing lots of digging to find out details on the different audio systems offered and want to share it as I have learned alot from reading on this board.
Here is a link that appears to show all the details of both audio systems. It is listed for the hatch, but after seeing the audio details officially released for the coupe - they appear to be the same.
http://www.babybmw.net/forum/viewtopic.php?t=6354
Hi-FI system = standard CDN system
Top Hi-FI = logic 7 upgrade
Another thing to note is that if you are looking to upgrade your system with an additional sub or more powerful amp - you want to get the base audio system. The reason is that the Logic 7 system has a digital output from the head unit that does not allow you to easily connect to an amp. The standard system speaker outputs are "line level" and you can easily connect them to a good quality amp.
The logic 7 amp also has internal crossovers that limits the frequencies on the various output channels. You will need to connect some other audio equipment (ie JL audio cleansweep) to have a full range of sound if you want to go after market.
If you are going to add a sub to the back you will want to order the ski bag (which i didn't
) as BMW has done a great job isolating the sound vibrations in the trunk. I have read that if you remove the ski bag cartridge it allows room for the waves to transfer to the cabin which creates bass. Some other options appear to be to get a bigger amp or to remove the rear fill speakers to allow the air to move into the cabin. Will have to wait till I get the car to find out the best solution.