"The dialogue will be more intelligible. In 5.1 channel mixes, all 5 main channels can be operating at once. With dense sound mixes, action effects can seriously mask subtle dialogue. In THX Home Theatre, you hear dialogue more distinctly, even in sequences with loud or complex sound effects."

I almost find the reverse of this to be true, I find the dialogue to be muted, or becoming lost?  I don't remember experiencing this on prior set-ups though?  I have always 'cheated' my center channel speaker though, turning up the dB a couple of notches after calibrating it using and SPL meter and AVIA, but I have noticed it more lately with the THX encoded tracks, I just found it curious?