Well, I just was alerted to an Over-The-Air (OTA) update two days ago so I updated my Galaxy Tab S to Android 6.0.1 Marshmallow and now it seems a little different again.
Firstly, I was not able to see any settings for Internet on the secondary account. That made me a little confused.
But finally when I switched back to the first account, I found the location is now:
Settings > Applications > Internet > Advanced > Save content to
The "Save content to" has two options, Device and SD card.