In the 8P you won't need the K line, diagnostics is done via CAN in your case. The hissing is normal because the RNS-E only goes into some kind of stand-by mode when you remove the key. That also explains why you don't see the boot screen. Sit in the car, open the window and then lock it via remote. After a couple of minutes you should hear the hissing stop and the RNS-E screen changing color. As soon as you unlock your car the RNS-E will wake up.