well i just tried talk designer- and for some reason it tells me the voice file is not supported and the file is in .wav format. plus in the drop-down there is only the option for .wav files so i would assume that is the supported format. and the xml files do not seem to support m3 for example( yes i am still working with gen3 characters).

i vaguely remember trying it before and i used simon, but i cant recall what format i used for the voice- i would guess it was .wav.