I have not built my sub yet, but according to WinISD I will definately need a SSF. This is the primary need for some EQ. I have seen SSF's in the form of an RCA plug, but have heard of no one using them. This would be cheaper and easier for me, but I don't know if it is the best choice.
By the way, the ED model is roughly the same price. Any reason for that one over the Reckhorn?