I made a two way center using two 400's with a couple of 10" woofers for my TSCM speakers in my theater. Used Selenium 220ti for the drivers and a 600 hz crossover with absolutely great results. I have a great timber match to my modified TSCM. I used a sealed acoustic suspension box and my rough measurements suggest my low frequency fall off is about 50 hx and the top is beyond my hearing.
As a second test I fed white noise from my Marantz to the TSCM and then to the center. The sound was remarkably similar. [Better in fact than my two RS-52 which you would think would be identical. I have checked close to a dozen sets of speakers with white noise and when compared they are distressingly dissimilar.]