Hi RIchard,
I understood your question Unfortunately, like I said, it is impossible. Both methods won’t work.
I have answered this in the dedicated DB4 topic as well a few years ago in the DB4 topic I think. You will indeed go crazy as it is simply impossible to make it work
DB4 needs drivers to be able to make its sound card and midi over USB work. A midi host like kenton does not have DB4 drivers. A direct connection will not work either.
But like I said you don’t actually need the sync. In the DB4 settings you can change the MIDI clock to internal, and then specify the bpm. Simply set the bpm the same as the DJS. Looping will work flawlessly because the clock of DB4 is very steady (and I recon that of the DJS is too.
So you only need to keep the turntables in sync manually, which you already do so no problem there