@unksskis the update stick is defiantly available. They probably don't let you order it online because they have to know if the update is compatible with your system, no reason to sell you an update that won't work for you. I recommend the new version 9. It locks in on the speed much faster than any other version. Also, the calibration is super easy, you click run and PP does everything. Send them an email with all of your system and boat info.
Edit: I don't have Zbox so can't comment on that. If you ski in the coarse at all I recommend the 3 event. If you only free ski in open water the standard version (Wakeboard pro) is just fine, it has a simple slalom mode.