I´m in an equal situation.
Had the Special Edition installed on an internal disc and didn´t want any interference with the exploration kit.
But it is very easy. You don´t have to install new Vienna players.
The only thing you have to do is plug in the new drive and run the Vienna Directory manager.
Add all folders with the instrument libraries into the Directory using the Browse function. ( I only left out the progarn files and manuals, that also come on the HD, since I didn´t want to confuse the Vienna player with that, maybe they don´t do any harm at all either).
All Done.
I didn´t test the special 180h Vienna Key yet. Because of the X mas deal I got me 4 new libraries, that actually run on my standard Vienna key, but the samples are streamed from the new exploration harddisc. With the whole library on it, there´s no need to copy and install the DVDs ( this alone maybe worth some etxra Euro for it :) )
Works out of the box, no problems.
Hope , that Murphy´s Law doesn´t proove me wrong, as soon as I plug in the 180h Key :) , but I really don´t expect any issues there.