OK so I've changed the path to have a capital F for Fonts, I've removed the default "serif" from the @fontface statements and I've recompressed into a new epub. The results are:
Adobe had no italics, and some ? instead of pinyin characters
My Iriver had the same as Adobe
Calibre had no italics, but showed the pinyin characters correctly
Stanza had the same as Calibre
Does this suggest anything to anyone? What other changes/additions have I missed?