There was a video bios available and I remember upgrading to the latest version a long time back. As for the XPS bios itself, I have not flashed it to A06....I seem to remember some issues people were having with it. I am not quite sure if those issues have been addressed by Dell but if they have then please let me know and then I will upgrade.
Groto maybe try asking the members nicely for some of the older revisions of the bioses like A04 and A05 and then once you are able to upgrade to those versions, then try upgrading to the latest version. I could be wrong but maybe your system is complaining about the jump from A02 to A06 which kind of does not make sense, but then again who knows how they write bioses at Dell!