Actually the ASUS site does not mention the X6 chips; the X4 PhII 965 is the newest AM3 chip they mention.
So it might work since the newest bios is dated July of this year.
EDIT: There is no electrical or physical reason the X6 chip would not work. It is all about bios. And the newest 1904 bios says it adds support for new CPU; but in the ASUS list of CPU they don't list any new chips that require that new bios. So it is a gamble... but the 1904 bios is probably for the X6 chips. I can't google any confirmation though.