Hi newcomer and welcome to the Tom's hardware forum.
No, you can not. If HP site says that you only can do a mirror with 500GB HD, maybe is because the chipset of the mobo don't support a bigger HD for mirror array.
Surprise. I talked to HP and they said it's possible to do RAID 1 for 2 2TB HD. I just need to down load Intel Matrix Storage software. For future reference, below is the link of Intel sw:
If you have any problems with motherboard. New BIOS V5.1 released for MS-7613, to enhance the stability and compatibility. Here's a link that will take you there..