Help with HighPoint Rocket 640L

I bought the HighPoint Rocket 640L controller card. The rest of my build is:

Mobo: ASUS M4A89GTD PRO/USB3 AM3 DDR3 AMD 890GX

RAM: Kingston HyperX Blu 8GB DDR3 1333

CPU: AMD Athlon II X2 270 Regor 3.4GHz AM3

PSU: RAIDMAX Blackstone series RX-700AC 700W Continuous Power ATX12V V2.3 / EPS12V

I currently have 5 3 TB Seagate Barracudas as 1 Parity+4 data drives, and a 1 TB cache drive I'm running apps like MySQL on (and I transfer about 120-200 gb per week to the machine). The machine boots fine, and everything works perfectly, but the drives I have fill the 6 SATA III slots on my mobo, so time for an expansion card.

I bought the Rocket 640L and hooked it up. Without any drives connected, the system boots fine. I can boot into the bios for it using CTRL-m, but if I connect a drive to it, somewhere between the initial mobo BIOS and booting into unRAID, a red LED on the MOBO goes off and the machine resets.

What are the steps I should be going through to troubleshoot and hopefully get the card to work? Or is it even worth the hassle, ie should I just return it and get a card that "just works" with unRAID?