The x series look to be pretty new. Couldn't find any real reviews but they look interesting. Configuration-wise, x-sls ~ M40, x-ls ~ M3.
All the speakers seem to have slightly deeper bass response than the corresponding Axioms, but if you have a decent sub I don't think that matters so much. If you're listening to music without a sub, the x-sls speakers might be preferable (I really like my M40s) although it totally depends on how good the midrange and treble are and you need real reviews or A/B listening yourself to tell that.
I found an audioholics "intro" with some pics :
audioholics
