HP specs (https://support.hp.com/us-en/document/c03028604) shows that an i7-2600 (95W) is supported. The i7-2600K is essentially the same CPU, but unlocked for overclocking. So, yes, you can use the i7-2600K. However, you might not be able to overclock it. It depends on the features in the motherboard and bios. My guess is that HP doesn't add overclocking features for this type of pre-built.