Most male voices fall into the 80-160hz area fwiw.

darbo, I do understand what you're inferring(right or wrong, I don't know) in that when you add other low freq's by means of a lower crossover it can affect other, slightly higher freq's as the speaker is doing more work(that the sub could/should handle). Do some experimenting, it's possible if you remove the lower, under 80hz freqs, then the centre can in fact, play more clearly in the 80hz+ region where male voicing is prominent.

Half of communication is listening. You can't listen with your mouth.