I have already done research on this and other forums and it seems that the alpha channels don't work very good with the mix8.layer. I turned on "export with shading engine", but no good. I read somewhere else that a Surface Shader in between should do the trick. I tried the following setup:
The targa file connects into "out Color" and "Out Transparency" of the surface shader and the surface shader itself connects from "Out MattOpacity" into the Color node of the mix8.layer. Again, no good! In this case nothing works, the targa file now doesn't show up at all.
Other threads talk about the p_maya_shading_engine, but I can't for the life of me find this shader anywhere. I know the author is known as puppet on the forums and I have even been to his homepage, but I can't find this shader anywhere.
It would be great if someone could help me out on this one.