So currently I am using the Avermedia live gamer portable usb capture card to capture PC gameplay. It is really good because I can play over DVI at 120Hz and still record using HDMI. Anyway I noticed that it has an analogue audio out port and thought that I would give it a go. I was absolutely thrilled when I first listened to it. There was no loss in quality vs my motherboard audio (the Supreme FX IV solution from ASUS) and I no longer hear my gpu whine at high frame rates (500fps or so in game menus) anymore. Free DAC with my capture card FTW :)
Edit: My headphones are the Audio Technica ATHm50s