I wondering where can download the soundtracks for the Bioshock 2? Or maybe upgrade the game edition?
There is a soundtrack available on iTunes featuring many of the licensed tracks from the game, for all the other licensed music, check out this page and do a little bit of hunting in iTunes.
As for the orchestral score, that was only available with the Special Edition of the Game. The only thing you can do there is hunt around on eBay or Amazon.com and try to find a decent price on a used copy.
I have the special edition of the game if you're interested. It comes with both the Bioshock and Bioshock 2 soundtracks.