I'm not so sure about squarewave testing being meaningful. It will reward first order (analog) x-over designs, but the audible benefits are debateable. I won't take sides in that debate, but Siegfried Linkwitz has written extensively on the subject, and he comes down squarely (pardon the pun) on the side of higher order designs that won't fare as well on squarewave tests.
Linkwitz certainly qualifies as an authority, since the Linkwitz-Riley crossover solution (even order only for "true" L-R, odd order "quasi" L-R is possible for 3rd order and above) is pretty widely considered a classic bit of design theory. Obviously, there are great designers (Dunleavy, Vandersteen, et al) out there using first order crossovers so.....
While L-R is NOT universally accepted as an optimal solution, Linkwitz's analysis does cast some doubt on the real world benefits of goood performance on a squarewave test.
Marty
PS For those pointing out that THD tests, etc. are of limited utility in judging a speaker's performance, I'd say that this is one more example where test results for speakers may raise more questions than they answer.