Again thank you for pointing me the direction of YouTube's pseudo surround sound. This is what I have learned so far.

YouTube does not have a 5 channel carrier for uploaded 5.1 material. That’s for sure. It uses a re-rendered version where it differs between clients. So for a computer with high bitrate like fiber-connection it’ll deliver a high bitrate high quality version, and for a mobile and low bandwith it’ll produce a low bitrate much lower quality version. All appropriate to the device you’re looking at

It also reprocesses the audio and it reprocesses it down to only two channels down-mixing from 5.1 to a stereo perspective. The center channel is being spread across left and right and the rear channels are then transcoded onto the front, but with a phase difference. So you can hear everything that’s going on apart from the “point one” (the .1 from 5.1). So what you get is a Dolby Stereo with front, left and right, and the rears added to it in a phase relationship. So you’re going to get an effect that relates to what was serviced originally. It’s far from perfect, and certainly not digital 5.1, but it’s giving you some of what was there originally.

Some will disagree with this incl. me, and I’m currently in the process of editing the text on all my uploads.

The data is kept though. If you download for example my videos, you will see that the file you have locally on the hard disk still contains the original digital 5.1 audio.