You are correct you need to uninstall Master Collection CS6 and then run CS6 Cleaner Tool (http://www.adobe.com/support/contact/cscleanertool.html?promoid=GYTAU)
Then install all the software through Adobe Application Manager.
So are you saying there is no way to have a loca lbackup of the install files or order a media dvd set for this, as downloading each time is not clever at all.
I would have thought downloading the cs6 master suite trials or ordering its trial media kit could be installed and enter the CS Cloud Sub serial and it activates it.
I just tried this with the downloaded cs6 master trial media on my new z800 and no it doesnt accept the serial, even though is a genunine serial.
Seriously Adobe how did you miss this one, such an obvious task user were going to try.