I would take the XXX over the MX anyday of the week. To many people have mechanical issues with the MX. I have practically heard it on every video with someone running an MX on here or other sites.
And if a XXX can't get loud well sounding insanely good, then you fail at the audioz! Personally have seen 1 XXX 12 do 147dbs on an older TL in 2005 off a 2k amp and sound awesome! I would love to rock a couple XXX's or hell even one.