Audio and video problem raspberry pi 2

Hi guys , i’m new in this world and i just finished last night configure my raspberry pi 2 with osmc. I got two problem the first one is my receiver is always changing audio input to stereo at every preview and i cant find how to chanelge the audio output to 7.1 ( my home theater setup ) by defaut the output is 2.0 … My other problem is my movies are rip by any dvd who works well but when the preview finish and the dvd menu wants to pop i lost the image but still have the sound . I got a grey or funky screen and nothing works . Can somebody can help me on this ??