Based on my experience with the X2's, I'd say that off axis the X series sounds very good, partly because they are fully OB so they fill the room with sound in a very pleasing way that box speakers just can't match.
And, bonus, when you DO sit in the sweet spot, the sound 'locks in' and elevates to an even higher level.
So, whether you are in the sweet spot or not, you're still getting absolutely world class sound.