I can only say that to date, for this high end stuff, neither VIA nor Nvidia have been very interested in linuxbios. Historically, VIA has been friendlier to linuxbios than most vendors, however. They have certainly been helpful to users of the EPIA series.
What you can try to do is ask each vendor for the linuxbios support you need if you use their part. Ask for docs you need to make the part work. Don't make a decision until you are sure you have all the docs you need. You can even try to get sample bios code for making the part work.
We'll help you if we can.
ron