Originally Posted by Mindrunner

Is this possible on DMM, then? Exchanging dupe Golds for 6* tickets?

Not so easily, but yes. Higher quality units and equipment can be traded for Bond Crystals. Those Bond Crystals can be exchanged for Dancho Medals, which then can be used for a 5*+ ticket. If you don't get a rainbow from that ticket, you get 30 Rainbow Medals. Once you get 300 of these, you can exchange them for any 6*. This should be the gist of it.
The exchange rates are quite high, so a lot of grinding is necessary to get from dupes to a free 6*.