Netflix including DD5.1 can be downloaded using Flixgrab. Just buy the license it's not expensive and is currently supported and works.
Download FlixGrab (WORKS w/ DD5.1 - need to buy)
https://www.freegrabapp.com/flixgrab
As for Amazon it is more then just cookies, they are using Widevine 2 protection which requires duel keys (hardware & software) so no cookie hack is going to get WVD working.