I am thinking that most of the people who are able to multibox heroic instances failed a heck of a lot before they started having regular success. I'm leveling a hunter at the moment and have left the multibox team aside, but he is nearing 60 (52 now, 12 levels in three days o.O) and he will replace the priest when I hit Outland instances. I'm sure I'll have plenty of painful moments as I learn my way through instances, but if it was easy it wouldn't be nearly as much fun.