low bass without giving up mid bass

I was thinking of attempting a build using a Fi IB318 v2 in Infinite Baffle being 5hz-45 and two skar SDR-8s in separate IB being 45-200hz (The rest of the system would be four 6.25's and two 1.5's). Is it possible to phase in any way to achieve a solid sounding slope from 40-60hz with this...