Does the DUO2 just have a plain old pinheader? If so you should be able to drop the X2 on there. You'll need to wire up the D0 (and HDD/LAN wires if you want those LEDs to work) but a pinheader's a pinheader. If you don't have all the pins to fill the X2 socket you may still be OK, just be sure you have pin 1 lined up right.
Now if this is a no-solder adapter there may be internal wiring that could cause problems. I would be careful about going forward.
-Whoopin'