Hi there, interesting read by Chew* but he didn't find it easy!
Now at first I would like to note that I was a tad dissapointed as my system would refuse to boot at rated specs of 7-8-7 even with adding voltage. It would however boot at C8, persistance pays off however and in the end I was victorious.
He was also using a Mobo with the 790 chipset not the 890 that you have which could well make a difference to the settings that you will need to get the RAM running at the specified rating.
Also, having done some further research into the subject, I have to admit to the fact that this problem is likely to be resolved with better BIOS, but until AMD and the Mobo manufacturers get their act together and release updates, I guess it is something that we have to work around in the short term.