You absolutely don't need a DAC/Amp combo for those to sound good. Can you dump loads of money and hear an improvement? Sure, should you? Only if you plan on moving to harder to drive, or more resolving headphones that are amp dependent.
If your primary use is for gaming, save your money. If you plan to do analytical listening then consider an amplifier, but you most likely don't need a DAC right away, unless you're playing on a very old PC. If you do get an amp, avoid the E10k and go for something like a Liquid Spark or JDS Atom for $100, and then add a DAC later if you need one. Don't fall into the tube hole until you've had a chance to audition one, and especially not for gaming where you want transparency.