I was long time Logic user when they were still supporting PC. Multichannel out are supported in 5.5 version, although it is a pain in the a** and won't work for every instrument. Frankly, I haven't tried EZD in Logic, but generally, first thing is that EZ drummer should appear in "multichannel" list when choosing a plugin. To do this on most VSTi's first you need to open instrument as a standalone before opening logic and choosing multichannel output configuration as default so the logic can recognize it as a multichannel plugin, or you can try to open same VSTi as stereo plugin then choose output configuration, close the plugin, and then after that hopefully it would appear in multichannel list. When and IF it appears like multichannel you then have to make outputs for it in logic's enviroment, by making audio objects and defining them as aux channels that can be used as outputs for the instrument. (it was quite a long time since last time I have worked in logic in logic, I hope I am telling you right thing) Channel where instrument itself is loaded will be outputs 1-2 and aux channels will be other outputs.
Problem is that it wont work for every instrument, it wont work everytime it may not work at all. Logic is very problematic about it, for instance, at one occasion it just stopped recognizing ANY of my existing plugs as multichannel, for no reason.
Give it a try, but it is very possible that you will be unable to make logic recognize EZD as multichannel VSTi...