I think the first initial batch of boards claimed (or at least the site claimed) to support the conroe chips. This was revised on the site with a passage asking customers to contact ASUS for a bios update because of an issue with chips not working on early bios revisions.
There are other threads I've read on this forum confirming this, even when ASUS claimed that certain chips would work on the board, they clearly would not post at all on older bios versions. On first try it seems a lot of the boards shipped with bios' earlier than 0701 had serious issues in picking up some of the chips, especially the extreme editition chips.
The board I bought the other day shipped with 0701 and my E6600 went straight in and worked fine, my mate who bought an E6700 however had to mail off for such a bios update.