Finally sold the Traktor Kontrol S4 Mk 2, which puts me back in the black on my stupid idea of figuring out what I need in a DJ controller by buying a bunch of broken ones, fixing them and selling them so that I can try them out without paying anything! I have made a grand total of like $50 USD now (turns out shipping and bad purchases early on ate up most of the profits, but the goal of learning more about controllers was still accomplished at a slight profit!)