I don't login that often sorry for the slow reply, you have probably solved your problem one way or the other by now. I'll throw down so other details about the BMC updates that helped me with this configuration.
My hazy recall from a year ago about the BIOS update was that it would flash 00 at boot then the 00 would disappear after a short period of time.
My board shipped with BIOS V1.3 and BMC V1.1
downgrade sequence was:
update the BIOS to V1.1 through the IPMI which was as simple as logging into the IPMI web interface selecting the file and pressing update.
The 1.1 version of the BMC (IPMI) is pretty basic it lacks any proper fan control so i emailed Asock Rack about the highest version that will work with the 7551p. They informed me that it is 1.16 but because of an AMI update at version 1.12 the only way to upgrade to 1.16 is using socflash, Asrock emailed me BMC V1.16
I had already gotten a copy of BMC V1.11 before i talked to Asrock. after my conversation with them i decided to update to 1.11 though the web interface then use socflash to get it to V1.16
The 1.11 version has decent fan control settings which for me was the main thing that was missing.
I tried to socflash V1.16 but after a few attempts (waiting 2 minutes for every reboot gets painful) i decided that BMC V1.11 does what i need and i just needed to get this machine back up and running.
I have tweaked a lot of settings in the bios so i though that one of my bios changes might be preventing the socflash comunicating properly at some point in the future i may try installing BMC V1.16 again after i factory reset bios, we'll see