Inasmuch as software has moved on since 2008 when I wrote about When Ant is subsidiary to <oXygen/>, I now run XSpec from <oXygen/> using the Ant bundled with recent <oXygen/>.
Bundled Ant means (almost) no extra downloads, and the recently added The only extra download is ${ps} editor variable for the path separator for the current platform means that a single “External Tool” definition works for both Linux and Windows (where
saxon9-ant.jar, which I added to my <oXygen/> installation so I could use a Saxon-specific Ant task. You can still run Ant, but not the Saxon Ant task, from <oXygen/> if you don’t have it, and it may yet come with a future release.