Sidegrade from PT10 to PT10 HD, possible?

Hi all,



It's likely that it's in a post somewhere, but my Google-fu is horrible today.



Is there an upgrade path .. at whatever price .. from ProTools 10 non-HD (using just the audio output hardware inside the MacPro), to ProTools 10 HD (also, hopefully, using just the audio output hardware inside the MacPro, for now)?



I suppose now the path would have to be from ProTools 10 non-HD, to ProTools 11 HD?



Or once you're stuck in one "family" you can't get out unless distinctly starting in the other "family?"



The price difference for starting over is rather steep, was wondering if there was a way I could extend my investment.



Thanks very much.