I'm thinking the 558's won't do you so well when it comes to gaming. All gaming sets I know of are all closed cans, while those Sennheisers are open-air type headphones. Yea, you'll get better sound quality, but from what I've heard, turning up open-air headphones to a certain point means you might hear an echo.....not 100% on that, though. But I still think closed cans will do you better.
That, and open-air don't isolate sound......at all.