From your motherboard specs page:
8 x DDR4 DIMM sockets supporting up to 128 GB of system memory
4 channel memory architecture
Support for DDR4 3333(O.C.) / 3200(O.C.) / 3000(O.C.) / 2800(O.C.) / 2666(O.C.) / 2400(O.C.) / 2133 MHz memory modules
I would personally recommend getting a new pack of 4 8GB cards. Your CPU can certainly handle RAM all the way up to 3333, but the sweet spot for price-to-performance right now is normally at around 3000Mhz. I recommend the 4-pack because it will make use of your motherboards quad-channel memory architecture, giving you the best performance.
Memory: G.Skill Ripjaws V Series 32GB (4 x 8GB) DDR4-3000 Memory ($194.99 @ Newegg)
Total: $194.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-10-24 16:51 EDT-0400