It doesn't look like you've got much heat-sinking on those drives, but if they fail right away, then heat's probably not the issue. Have you tried tuning the drives, using a fine screwdriver to adjust the trimpots? It's recommended to use an O-scope to do this, but trial and error can also work (eventually). There's info on how to do it on the Gecko site, but here's some more advice: Fabrications of the Mind: Tuning EMC2 and Gecko servo drives
I'd disconnect all but the one drive I was working with at the time, just to narrow things down. And if all else fails, you can ask Gecko for help - they're amazingly good about supporting individual users.