Hi Infinidie,
If you have the 2007 DNA, all DNA's came out with the same sized bar, they were totally interchangeable with all sizes. We opted for bigger bars for the 12m to increase the turning speed but other than that, the rest were all the same bars.
I think the 2008 DNA's came out with different bar sizes, but the 6m and 9m share the same bar size, the 12m bar was upgraded to a longer bar from standard. The 12m came standard with a 55cm and the 9 and 6 with a 45cm.
As the boys said, the DNA bar functions best with the cleat on the chicken loop as at the end of the throw where the pulley is, would be far too far to reach on another bar setup.
Ask around, I know of a few people who have broken lines and replaced the set and have spares laying around.
And the answer to your final qustion is YES, the bars are interchangeable between models. If you are after a 12m 08, we are selling off our old school kites and I also have a brand new 12m in stock for sale.
Good winds,