They seem to have the shallowest well of rim manufacturers which makes tires super tight to put on.
Make sure the bead is pinched together and as far in the rim as you can get it around the opposite side of where you are trying to put it over the rim.
I wear long fingered gloves or mechanics gloves to work the bead over as much as I can.
If I have to resort to levers I just use them to lift the bead and press it over with my other hand to prevent pinching the tube and putting holes in it. Don't use the lever to pry the bead over the side of the rim. Just lift and push hard a couple inches over.
broke a tire lever today trying to mount up some heavily studded Nokian Gazzy-G's on my 823's. I blame it on the cold. Took bringing them inside to get the bead to seat even with 60psi.
By far the heaviest wheel-tire combo I've ever held. 823's + Hadleys + Nokain Gazzy-G+ Hundreds of SelfTapping Sheetmetal screws+ heavy as **** DH tubes + Duct tape covering screw heads from inside. Oh well, i'll have traction for the snow race at Blue Mt. on Saturday!
I have a hard time putting on tires too. I have Azonic Outlaws with Maxxix DH tires. I always use metal Park Tool tire levers. I hate those plastic ones. They work one time before they bend or break.
My XC setup is hard to put on too. Azonic Outlaws with Kenda Tubeless tires.