Hello @scoottttay
Some of the memory finder suggestions are definitely off base. Your motherboard will only handle 2133 Mhz ram.
Anything faster will get clocked down to meet the default speed. I Do Not recommend mixing one of those with your current stick. 2x8GB sticks is what the specs say are compatible. I don't know of anyone testing the idea of 16GB sticks. You could try, but if it didn't work, the store most likely wont take your ram back.
I believe Crucial has an 8GB stick that is rated at 2133, I would use that one.
Or you could always run a tool like CPUz and see the timings of your original stick, then find another one with the same timings to match it. This will enable dual channel capability and help ensure compatibility.
Example:

Let me know if you have other questions.