I'm trying to remember ..... how many 500 units you can get into the rack mount power supply? You have to purchase that as well you know. And there was problems with enough power to muti units but that may have been resolved.
As I understand it, you can put 6 500 units in the API 500 6B. There are some 500 units that have to be wired differently. Hopefully, I don't run into that.