I've looking for headphones to buy for almost 5 months now and I still cann't make up my mind. I'm torn between the Sennhiser HD 558 and the ATH-M50 (and, although with less enthusiasm, the Sennheiser HD 439). I really like the sound of my great sounding and unbelievably uncomfortable AKG...

How easy, risky and worthy is it to buy a set of headphones and have their drivers replaced? I'm considering to do so, but I'm worryied about damaging them irreversibly, expences and just the time to find someone who can do it well. Have you tried it? What do you recommend?   And what drivers...