I'm not sure to be honest as I've never connected my Techs to an S4 (my roommate does own one though). Everything is plugged in through my mixer.

I'm not sure how the S4 handles the tables, I'm assuming the S4 would handle 2 decks of transport, and then the turntables the other two? So you'd have the jogwheels on the S4 controlling A and B and the tables controlling C and D and use the S4 for the mixer portion? No clue how it works with the S4.

You definitely don't need to buy new Technics though. When people say they are the best and built like tanks they mean it. I bought 2 used Technics 1210 mk2's and they are in great working order. I was lucky enough to get 2 units that don't have a scratch on them. The X1 is the absolute best controller to use alongside a DVS setup though. I'd maybe even get one even though you have the S4 so that you don't have to switch back and forth between decks on the controller and get confused.