The tek.drum and tek.wave have only one 3.5mm stereo jack. There is a small switch at the back that allows you to select either duplicated mono on both channels, or receiving sync triggers on one and sending audio on the other. I you use a splitter cable you can send triggers into them, while sending the audio to another device. The .hub works in the same way. With a splitter cable you can connect and sync a volka. You plug the stereo jack into the .hub, one splitted mono out to trigger in on the volka, and one to audio out of the volka.