I believe he is suggesting that the problem is on the PC side using the site, not that the stick doesn't do 5.1.
There are a number of restrictions regarding 4k,HDR,Atmos etc.. put on PCs. Mostly it requires Intel based chips, motherboard and graphics. Not that you cannot do 4k,HDR,Atmos on a PC, just that impositions prevent plugging in a UHD drive and disc or Netflix/Amazon and getting said.
