Each Oculus hardware platform has different audio capabilities.
DK1 does not provide any audio output and thus relies on the end user's system for audio output.
DK2 also relies on the end user's system for audio output, but adds positional tracking.
The Oculus CV1 HMD has a built-in DAC (audio over USB connected to the headset) and ADC (for microphone). The audio subsystem is class compliant and supports Windows, Mac and Linux. The HMD has integrated headphones as well and a microphone.
The Samsung Gear VR mobile product supports 16-bit, 48 kHz sound. Like DK1, it supports head orientation but not positional tracking. Headphone choice is dictated by the end user.
Mobile performance is significantly lower than desktop PC performance, so try to minimize the number of audio sources.