I recently went through the same thing, and started w/ powered speakers. TBH, the first thing I did was re-rip CDs into ALAC (I'm a Mac user), then I spent $500 on a Apogee Duet (DAC), then bought AudioEngine A5's (powered speakers) for $350. Well, after a month, I dcided to upgrade!! Sold my A5's on another forum for a minimal loss. I then bought a Music Hall A25.2 Integrated amp, Epos ELS-3 bookshelf speakers, and a Hsu VTF-1 powered sub. Given my room (~1500 cubic feet), and the fact most of my listening is nearfield, this setup is pretty darn good--sounds terrific, IMO.
If I were you, I'd consider first what you point out anyway--the actual music source your listening to. And, again, just my opinion, it might be worth your while to take a look at an external DAC (USB or optical) as well.... I can't even describe what a difference the Apogee Duet made in sound quality, and Macbook Pros are said to have decent native audio capabilities.
Not to sound snobbish, but your consideration of B&W speakers for this application indicates you have really good taste!!

I'm a sucker for English speaker companies (heck, I bought Epos after all, even though they're the low end)... I'm just wondering if those would be the best speakers for nearfield listening?? Or am I assuming too much that's what your listening position would necessarily be?