Bitstream.  PCM from a TV is almost always 2.0 stereo.  If there was a “Passthrough” mode, you would select that, but Bitstream is the choice when there is no Passthrough.  That will get you the Dolby Digital 5.1 coming from the Sky box. 

Thanks , if I decide in the future to connect the beam via optical , the digital output has pcm or bitstream , should that be on bitstream too ?? 

Yes, but I don’t know why you would.  ARC is superior to optical. 

Thanks , it would only be because if I want to listen to the TV speakers I have to turn off CEC .

I may be an outlier, but I’ve never found the need to switch back to crappy TV speakers once I’ve heard proper surround sound.  I just don’t get it.  Then again, I have a sister who once said “I can’t hear the TV, it’s up too loud” and made it sound logical, so what do I know?  

Its the wife , she likes to watch her soaps with normal TV lol