No alpha channel would be  great and preferred.Transparency is just what they are called, most are all alpha now. They were probably created as an alpha, which is better.That usually just involves a reversal of color, but only if the trans color is not black. I don't use poser, these come fro D|S, however, I don't see an issue w/ the files that are output the paths seem correct, but only transmaps don't make it. You can call them alpha maps, but now they all basically mean the same thing.

No need to think outside the box....
    Just make it invisible.