Help connecting PBX headphones to AUS ROG STRIX

Hey all, I was hoping someone can help me connect my son’s PBX Raptor Pro Plus HD gaming headset to his Asus ROG Strix GL10DH computer. (First off monitor has no built in sound) . I was able to get the mic to work but can’t hear anything out of them. I’m having a very difficult time setting it up. It has a combo audio/mic on front and Mic in and audio out on back. Headphones show Combo and includes splitter so I’ve tried using a splitter doesn’t work. Please help.