Get 2 long, preferably t-handle allen keys. Good quality allen keys. And reef on them. It takes quite a bit of force to crack a King axle open, far moreso than would be proportional to the original tightening force. I guess it has something to do with super-fine aluminum threads and the locknut assembly, but this has been my experience with the dozens I have rebuilt.
Is it the bearings or freehub that are feeling gritty? The bearings can be rebuilt but require a special tool to remove, and the freehub will require fresh Ringdrive lube once cleaned out. So you may have to swing by the LBS for either of those anyway. But when it comes to the axle, just crank it.
Andrew
www.cycle-solutions.com