I don't think so as you have the only setting in the box set to surround, unless there is a setting in Netflix itself. As this is an app issue you would be best seeking an answer from Netflix themselves as they supply the app for the box.
Can you get Netflix on other devices? Do these broadcast in surround sound?
Found this in Google but not read it. Does this help? Seems there is a setting to use within the apps available.
Please remember to mark Solved Posts with Best Answer. Doing so helps others and saves OCE's time to look at unsolved topics. Thanks, Steve.