OK, these mobos are close enough to each other to share most code. Let me throw out a challenge to this group. Make the bios image that runs on each board *IDENTICAL*. You can figure out what each board is -- can you tell by which superio it is or something? -- and then case out in runtime.
Why is this good? Because a vendor can see that with proper design, a single bios image can support many mainboards -- even if the hardware differs slightly -- thus reducing the cost.
We've talked about this for years, never done it. Is this the time?