Okay I think I've solved my audio issues.... was just a case of wiping the drivers a couple of times... perhaps it's "burnt" itself in?
Now I'm just left with my webcam not being able to be used in any desktop apps, but working fine in the Metro "camera" app. Have tried downloading latest drivers from Logitech website, using auto-installed camera and USB Video standard driver as well but all options exhibit the same "works fine in Metro, but not in any desktop apps" problem. It feels like a case of Metro stealing the camera's focus and not letting anything else use it, can't find any options I've tried the Troubleshooter -> Hardware + Sound, as well as looking through as many options as possible. Crazily within XSplit I can even get into the Logitech driver software from the Configure button, but it still won't output any video feed. So it definitely detects it, it just won't damn well turn it on outside of Metro.