Only asus can tell you what processors are compatible with their board.
Please contact asus support.
This message was posted on behalf of Intel Corporation
Al_Hill thank you for the help.
ANJUNHONG I checked the supported CPUs for this motherboard here; P8H67 | Motherboards | ASUS Global, but I do not see the Intel® Core™ i5-6600 Processor (6M Cache, up to 3.90 GHz) Specifications listed. The Intel® Core™ i5-2500S Processor (6M Cache, up to 3.70 GHz) Specifications does seem to be listed; however, as mentioned before try getting in contact with ASUS for more information on the compatibility for these processors.