We have received 2 Intel Nehalem E5504 for testing. We have installed it onto your X8DTL-iF and we can see 8 cores. But Nehalem was supposed to have Hyper Threading (HT), so 16 cores should be seen, we are using windows 2003 enterprise server, which can handle 16 cores?
You are using a CPU out from the "value line" series CPU, and it has no Hyper Threading (HT). Please use "Volume" or "Performance series", like E5520 and up which support HT.