Make sure you've installed VR services: https://play.google.com/store/apps/details?id=com.google.vr.vrcore
And also cardboard: https://arvr.google.com/cardboard/apps/
If the QR code still can't br scanned, try to change display settings manually. That's what I did because my QR code wasnt working too.
You can also try to Google for the QR code of similar headsets and try to scan the picture of the QR codes.
Yes there is, I use a app called wirelles speaker it works, you might have to open ivry first then the other app or vice versa I don't remember exactly in order for this to work...
https://play.google.com/store/apps/details?id=com.vnd.wifi_audio