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i was happy that i was able to tranfer all my PC runtime into Mac with no problems whatsoever, but since now i'm thinking of maybe moving to Daz Studio 3 for mac.. will i be able to move my Runtime there with no issues? because i always see Daz has its own installers, but i wonder if something that has already been installed in Poser will be able to run fine on DS3...

you can link your poser runtime to DAZ studio and everything will work fine, no need to move your runtime, if DAZ has installers for DS though you should install those as well, as those generally contain Studio optimized material presets. (newer installers combine them generally as Studio can now read the studio presets from the poser runtime if there is a poser mat pose of the same name in the same folder).