I believe the recommendation is to start with one of the boards
closest to what you have (ie. one of the boards with the same
northbridge, southbridge, and superio), try to figure out any
adjustments you can tell it needs and test and debug.
The northbridge is part of the cpu and depends on which cpu you
install. For the fx series it would be agesa family 15tn. I'm not sure
how the cpu support works, depending on your build, you may only get
support for certain processor families? I don't think the agesa code
is very well supported.
You posted your flashrom log in place of your superiotool log, but the
manual says it has an ITE superio. There are amd sb700 boards on
boardstatus with either the ITE IT8712F or ITE IT8718F.
For flashing you would need a testclip and something to drive it. The
dual bios feature won't help with coreboot, since it isn't jumper/
hardware switched based that I can tell.
I was going to mention needing to figure out the option rom or
graphics init for the onboard graphics, but it looks like your using a
separate video card, so it can probably be ignored.
Hopefully this helps you and I didn't get too much of it wrong.