As far as compatability is concerned, I would stick with one line. I know for a fact that VPI and Joliff are not compatible. I've heard that VPI and SK are not compatible either. As for Joliff and SK, I have not heard of much documentation or attempts at this breeding, however, I would imagine that they aren't.

Also, from time to time, you may also here about D&M line Axanthics (which I don't think they were ever tested for compatability), and you will also hear about NERD line Axanthics (which are compatible with VPI line, so I'm told).

Hope that helps a bit.