I have a new 1613 receiver with 3 speakers configured + sub(no surround speakers). In dolby digital , the center channel always sounds restricted(missing lower and very high frequencies). When switching between dolby digital and stereo listening modes, the sound in stereo is a lot clearer. I assume that when switching to stereo listening mode, the material from the center channel is simply distributed to the left and right speaker. The problem seems to be unrelated to dynamic eq. It exists with dynamic eq disabled and even in pure direct mode. It seems like a dolby digital decoder problem.
It may be just the way dolby digital works, I am not sure. I do not have another receiver to verify that.