https://help.hbogo.com/hc/en-us/requests/new
You'll have to be already registered with HBO Go and enter your ID. I submitted a request asking them to implement 5.1 DD on Android TV.
Hopefully if enough of us are active HBO Go users, they'll listen and update ASAP!
I have Dolby Digital 5.1 in HBO go. Amazon is the problem for me.