Connect a standard 3.5 mm AUX cable - one side connects to your PC audio output and the other side to the Strap’s audio input jack. Next, connect your headphones to the Strap audio output jack.
On your PC - go to "sound settings" and make sure your main soundcard is set as default.
Otherwise, the audio will be routed to the Vive headset.
Note: please remember to always set your audio source to MAX volume.