I have a definite answer for one of your questions and a more hesitant answer about the other.
The plural of 'axis' is 'axes' (ax-eez). That's definite.
As for zeroing out the rotation... what about this. Figure out what the joint's 'default' orientation is, and then just manually slide your X, Y and Z curves up or down to adjust for that. So for example if you find that when you connect the curve to the joint, it jumps +10 degrees on X from where you want it to be, simply grab your curve in the Graph Editor and slide it down by 10 units and you should be fine.
If you can't edit the curves themselves, don't forget you can use math nodes in the Hypergraph to add or subtract from a curve before outputting to another node.
Someone else might have a better answer; I'm a little out of my depth once we stop talking about pluralisation. 
Good luck.
-Steve