Same here. I've had mine for over a year and thought I had it down pat until I started binging on some Hannibal series blu rays. Mads Mikkelsen was very difficult to follow due to his accent and then I aimed my speakers just a tad more inwards and presto! I could now understand him.
It all boiled down to my tweeters being offset to the outside and I measured them using a laser centered right down the middle. What used to work for me resulted in the tweeters being a touch too much away from me.
It amounted to about 1 1/2" difference than my usual way of setting up but that's all it took for that turn for the worse. Even with music, the center is more fully realized and the music is a touch more dynamic even at the same volume.
All the best,
Nonoise