Sorry... I'd somehow missed the posts in which you mentioned you'd already tried stuffit.

For info, the file that you had an issue with here, I get the same issue on my mac... that is a .cpgz file being created when I double-click on the downloaded zip.

I also, for this one, get a .cpgz loop happening when I do right-click and "open with" Stuffit expander. So apparently same as you got entirely.

However, strangely, when I open Stuffit Expander from Applications, then select File->Expand, browse to the zip file and then browse to my Poser Pro 2012 Content folder, the contents are correctly expanded into my main runtime.

Anyway, nice looking character morph ;-)