I think you are right on the holes being too close together. And the box may not have enough volume to support them either. If the box is big enough I could always cut/grind away the speaker frame in the overlapping area where the circles meet. Depending on box volume I may just use a single 8".. I think it is big enough for that.. I'll know once I measure it. Do you have a recommendation for a 8" sub? I was thinking of going with JL but perhaps there is a better choice? I live in the Boston Area... custom sub up here was 1600-1800 installed. Seemed rather steep for my needs.