The JTR S1 actually puts a serious smack down on the JL F113 in this metric (output per cubic foot centered at 20hz) being ~5dB less than the S2 but only slightly larger than the JL. The size difference between the two may as well not even exist.
19.25x19.25x16.5 for JL
21x21x18 for the JTR. So not even 2" larger in any dimension (as in, even the wife won't notice unless they are sitting next to each other), but sitting around 107dB at 20hz. So 1 actually pretty much would beat two f113s.