Actually KHX and KVR are products for different positions. It should be easy to see the difference from the heatsink added and the way to use them is also different.
HyperX is considered as overclocking RAM, so you don't use together with normal RAM. But, you can use the HyperX by itself right? (since you can go in Windows, I assume it's working) But you need to o/c in BIOS to run at 800 for this memory, it's HyperX, it's overclock.
Your best bet is to swap for the same part# as your existing memory, it's the safest method to upgrade.
Just something extra for you to know, you'll encounter problems when using two memories with same SPD (e.g. 5) but in different frequencies (e.g. 667, 800). This is what you're currently experiencing.