There is a new version of this app.
It allows in a one step process to convert FCPX captions (CEA, iTT) to SRT, VTT and for those how do DVDs to Spruce STL and Encore Script.
Just drag a project from the FCPX browser to the app's main window. For multiple 'Caption Roles' you can convert all, a selection or only one. Styles and colors are kept for SRT, VTT, styles for SRT.
For small projects the app is free. http://spherico.com/filmtools/TitleExchange/XTCE/XTCE.dmg