Nothing is stopping you from putting any kind of memory in the slots.
Memory is guaranteed in the form sold. Other combinations you decide to make have no guarantee to be compatible with 2x Kingston KHX1600C9D3/4GX.
Kingston Khx1600c9d3/4g
https://www.ebay.com/p/HyperX-Genesis-4gb-Desktop-RAM-512m-X-64-bit-Ddr3-1600-Kingston-Khx1600c9d3-4g/25012862829?iid=183152530821&chn=ps
The part number, Kingston KHX1600C9D3/4GX, looks to be a single module. Modules sold as singles are not guaranteed to be compatible in multiples. You are free to do your own compatibility testing with no guarantees for combinations other than the form in which the memory was sold. Using "identical, exact match" are not guaranteed to be compatible with the other memory.