Audio :: Game Audio Not Playing Through Headphones?

When my Turtlebeach x12 is plugged into my computer (runs Windows 8) and I try to launch some steam games the audio plays through the built-in speakers rather than my headset. I've played around with default devices and disabling/enabling different devices, but nothing has worked. In some games like Planetside 2, the in-game option to set the output device to the headphones works perfectly, but in most other games (e.g. Left for Dead), audio still plays out of my speakers. When I disable the speakers there is no game sound at all. This also wasn't an issue on my old laptop that runs Windows 7. Is there any way to here the game audio from my headset?