Recently broke a rear axle on my 04 400 4x4 too, broke up inside the inner boot which made removal a bit more difficult. The axles are removed from the diff by tugging outward, it's that simple. Push the axle in towards the rear diff (there is about an inch of movement) and then tug outwards like hell! Sometimes it will pop right out, sometimes you have to repeat the process several times, but it will eventually come out. The axle is held into the rear diff by a snap ring that gets compressed when you tug on it and be careful not to pull the wheeler off of the jack. It might help if you position your feet up on either side of the diff.
Now, if you removed the large snap ring and pulled the inner end of the axle out of the housing (the end with the ball bearings) put it back together, replace the snap ring and do the above tugging process to get the rest of the axle assembly out of the diff. I had to clamp some vice grips on to the small broken piece of axle that was left and go at it for about 10 minutes, but it came eventually out. Some beer and/or excessive swearing can also help ease the process!
I bought a new AC axle assembly (completely assembled from end to end making re-assembly a breeze) from kenssports.com and all you have to do is push it back in and reassemble the suspension. If you haven't done so yet, drain the rear diff fluid and add 8.5 oz of new fluid once the new axle is in.
Just replaced a CV boot on my 2010 which requires axle removal in the same manner and the axle popped right out on the first tug!