There are builds of IMR with and without RAID-5 support. Some only have 0/1 and possibly 10 but no 5. I would extract the 8.7 that's there and compare it to the two we have (the ICH10 one and the ICH9 one I found) and if it's smaller then those, replace it with the ICH9 one I found... or possibly try a later 8 series release like 8.9[.1]. 8.7 ICH9 has a higher chance of working, IMO. And that's if it's even different from what's there.
Feel free to use/link/host any BIOS I post, no credit necessary. However, this is at your own risk and I take no responsibility. Always keep a backup of a known-good BIOS. Don't flash a motherboard if you don't have a backup computer just in case.
Always use RAID mode. RAIDFix
Always use RAID mode. RAIDFix