Well 'autorepeat ON' is the default behaviour - so I wouldn't expect that to be an issue for general usability. Your wxWindows code should be able to handle autorepeat - perhaps the issue here is that the delay value (the time interval before a single key press becomes interpreted as a key 'hold') is being misapplied?

However the fact that you apparently can't disable it with xset suggests there's something more general going wrong under the hood.