xxgdb -x filename objfile reports a usage error. -x filename is a legitimate gdb option, and should be recognized by xxgdb. This problem makes it impossible to generate gdb commands on the fly in a script and either invoke gdb or xxgdb depending on the presence of an X display.
Sorry, but xxgdb is pretty simple and lacks support for a lot of the features found in GDB. I'd recommend using ddd from powertools instead.