Probably not. Can you post an example with 5.1 audio. I have multiple Youtube sources, based on experience with Amazon prime only my Panny TV, Youtube app delivers 5.1.
I did a search for HD 5.1 samples on Youtube and got loads of Dolby Digital promos and tests and all were recognised as HD but all came through as stereo on the HDR. I know my HDR is set up correctly as I can play multi channel sound from my Harddrive and also the odd BBC HD live or recorded showing e.g. Doctor Who. I did notice that the BBC Iplayer also does not seem to send multichannel sound down the stream or that the HDR app does not support it, using Doctor Who has an example (although not available now) again. When Doctor Who was live or recorded in HD it produced multichannel sound but if sourced from the Iplayer it didn’t.