@Reese Excuse me, but I don’t know what you mean by “preview mode”, I can’t find such an option in the unit.
As I explain in the first post, working with the units autonomously, without software support, I think the only option left to pre-listen to the songs before mixing them is to load them on the deck. I also don’t know if there will be any combination of buttons to eject the track and empty the buffer at that moment.
What if I have in the settings of the units disabled (Off( are the options “Lock Playing Deck” and “Needle Lock”, but of course I have activated the “Track Preview”.