Hi David,
I don't think that it will be possible to drive two 2560x1600 screens with the DC53427. I got it and am currently having problems to even recreate the setup mentioned in the documentation of the DC53427 
(See here https://communities.intel.com/message/207071 )
Would be nice if someone from Intel could nonetheless test if it is actually possible to drive two 2560x1600 displays or not.