Dont need to ZIP it up..you can download as a .DMG file  IIS management - on the server - cfg the MIME type " .dmg "  to  application/octet-stream and then you can download it similar to the Windows clients
So, I should be able to get this working, but dammit, I am admitting defeat.  I've tried to get the app portal for MAC dmg file working with the Gateway download links and even with a base IIS 7 server and even though I the settings so IIS recognises the files, they don't work for MAC users (presumably because they are being saved using a PC... So, how does everyone provide a download link for the app portal client for MAC? 
Providing Download link for MAC App Portal software