Unfortunately you cannot "sync" the tempo at this point in time.
Please feel free to submit a feature request to the Product Development team here: http://line6.com/company/contact/productFeedback/?topic_id=3
at this time and at any time ... perry! don't play with our feelings ... line6 heared this wish soooooooo many times before ... then promises ... then new updates but broken promises ... then deleting theese threads where theese promises were made ... and finally after long accusing and pointing fingers the truth: that time sync feature probably never will be added ...
at least line6 came up with podfarm which gives a way to sync the X3 to DAW's by using additional software ... but that's not the same thing like midi clock or midi time code would be ...