Great question!! I don't have any hands on experience with that particular gear but I found a cool cheat sheet with suggested settings and Crazy Train is on the list:

http://line6.com/media/club/spideriv/SpiderIV75_settings.pdf

Another thing to try is to dial in a straight up Marshall style crunch sound on the Spider, then use a distortion pedal on the HD500x in front to get close to the sound.

Let me know how it goes!

Mike