You're sure the W7 ISO isn't jacked?
You have tried installing on a SATA drive rather than SSDs in a raid? (SSDs+raid=bad because of garbage collecting when I looked at it 6 months - a year ago... could be different by now)
You have put W7 on a jump drive with the Windows tool and tried to install from that?
Microsoft Store Online
It's strange that your computer is also going slow after the install. I would be leaning toward that hard drives here. I would unplug every HDD but one of the SATA drives. In fact, with everything you tried I would just put W7 on a jump drive, unplug everything but one stick of ram and one HDD and give that a shot.
After the HDD I would, like you, move to the MoBo. It most cases this would be extreme, but it would be my next move. Two weeks without PS2? Send back the mobo
Something like this has happened to me in the past, now that I think about it. It gave sort of a physical memory dump effect. The drive starts kinda slow, then gets slower, and eventually crashes. Tested the mobo, replaced the hdd... only to (eventually) find that replacing the SATA cable
fixed it. Such a strange effect for a SATA cable to give. Especially when restarting the computer enabled the computer to function like normal again. Only to slow down and crash...