thats the last posibillity. i tried several tools for mac. graphicconverter 7, squishDDS, gimp and ContentaConverterPREMIUM. no success. if i can`t find a working tool for osX i have to do it with bootcamp, and so on. because a custom reflection map is just essential to me.
the way through windows/photoshop&nvidiaplugin makes the workflow complicated. and makes it hard going..