Conrad Salier:

I have no doubt that Lord Zirn is your vassal and still under your command. However, as a Crusader Count, your command over him is somewhat limited. You can call him back, certainly, but you do not control his movements. Currently Lord Zirn is leading an Imperial force, and is thus subject to the Kaiser and the Kaiser alone's command.

Remember, the only armies that Dukes (and Kings of Outremer, for that matter) control are the House Armies.

I also question why Iconium is to be taken. I do not recall any Edict calling for its capture. I also know that it will not become part of Outremer, because the Kingdom is complete.