While the cub file used for the LX9000 airspace is a binary file, as long as you have a copy of SeeYou, you can create a cub file easily using the Mobile Wizard.

As JS says you sometimes want to build your own Open Air file using a text editor, you can still do that for the 9000. Build the Open Air file, load it into SeeYou and then export it to cub format using the Mobile Wizard - done!