I am not sure what firmware is need, it may even be V3 and above, you may have to troll through the archives to see when they changed to firmware that supported it, probably whatever was on the Naza_M V2's when they came on the market. I see no reason not to be using the latest firmware though, working well for me.
I am using V4.02 and it is working very well on my Disco Classic and Disco Pro.
Pete