All the XLS/XCS line is awesome, and the mounting capabilities near endless. I used them for several years as I kept creeping up the McLine of speakers. They are all in good homes now, with very happy owners.
The 80hz cross was on the original models, they stopped putting them on because people were cluelessly trying to bi-wire/bi-amp. That resulted in less than stellar performance. The new(er) ones just had a single set of binding posts to eliminate the confusion, so be careful if you put a MC501 or higher on them; you may fry the midrange (you'd probably never harm that Bessel array).
If you use XCS350's that is a 2-person mounting job. They are way heavier than they look!