Thuban is supposed to work on both AM2+ and AM3 based motherboards.
However it depends on the Motherboard Manufacturer if there is a BIOS update for it.
If an AM2+ motherboard doesn't have an update for the newer Phenom II CPU's rest assured that there will be no update for the upcoming 6 core Thuban CPU.
Those with higher tier longer support flagship motherboards like an AM2+ 790FX one stand a better chance for support.Thuban most likely will be a higher 140 watt TDP CPU so if your motherboard doesn't support 140 watt CPU's that would probably be another clue.