Greetings
The ADC can operate in non-Demux mode at the full rated speed.
Your observation is correct. Due to the 1 Gbps limition of the Virtex 4, the FPGA/firmware used on the reference board only supports operation in the Demux mode of operation. Therefore a minimum of 24 data pairs must be captured to acquire one channel (I or Q) of data. This is a limitation of the board only, not the ADC itself.
I apologize that this is not clearly documented in the evaluation board user's guide or other collateral. I will see that it is added in the next revision of the user's guide.
Best regards,
Jim B