Well the Kappa perfect build is really for the Infinity speaker. There are alot of variables to the design of your sub. I would say that no, 2 subs are not overkill ,(just ask Mike C
) In fact the more subs the merrier methinks. There are also quite a few very qualified sub and speaker designers on this site. Wmax and Averserfi as well as Haloeb and Warpdv...Go ahead and look around the DIY section of this forum and I think therein lies your answers. Best of luck to you and DIY subs are your best bet. The EP 2500 will power a pair of the JL's just fine....