Like we said in the cs:go pre-order article, Valve is going to bring out a lot of update before August 14th, and the first big one is a massive change to sound spatialization. If we take a look at the earlier versions of Counter-Strike, 1.6 produces stereo sound using a particular cross-fading algorithm for both headphones and speakers. And in Source (and recently in GO) spatialization is optimized for 5.1 surround speakers, and that signal is down-mixed when you use headphones our stereo speakers. Take a look at the image to get a better perspective about it.
So in the upcoming sound update you will have the possibility to configure your own preferred speaker placement and cross-fading algorithms. Valve also provides presets that are optimized for headphones, speakers and surround-sound setups. This should give new and old players the advantage to customize their setup to match their own playing style.