If I were you I would use the Picoblaze to talk to the A2D. I'm not sure how good at VHDL or Verilog you are, but the Picoblaze is an easy to use softcore CPU availible on the Xilinx Website. You'll write assembly instructions and connect the output/input port on the Picoblaze to the A2D. Xilinx has excellent app notes on how to use the Picoblaze. Good Luck.