I've been trying to get the Korg PadKontrol working with the OP-Z over USB for a week or two. Tested a few cables, and now tried a Kingston Nucleum USB hub.
The manual is vague (and indeed a few folk on YouTube using them with the OP-Z and being very very vague), but implies that the PadKontrol provides USB over MIDI for DAW. There are old drivers about, but given a USB MIDI device should be driverless on Mac OS, I thought I should check. And of course, it's not. I'm guessing it was some kind of proprierty interface Korg developed (hence the drivers) to provide three channels of MIDI input (an "A" and "B" from the PadKontrol interface and the MIDI IN port as "C", all to the DAW) and two channels of output (from the DAW to the MIDI OUT port, and the config software to configure the PadKontrol).
As the OP-Z is expecting a driverless MIDI device, this isn't going to work. A vague comment on a random video I found, and they commented that they used a 5-pin cable as they think their PadKontrol has a broken USB port. To expand, they're using a USB MIDI interface via USB (or the OpLab). Their USB port isn't broken, it just doesn't do a damn thing other than power the PadKontrol when connected to the OP-Z.
I've got an OpLab, so it's not a major thing, I can just use the 5-pin plugs and connect it that way... I may also be able to use the OP-Z as a sequencer, and the PadKontrol to play the OP-Z, and the OP-Z to interface with my Polyend Poly 2. That could be fun.
Now here's the weird thing. My Polyend Poly 2 works with the PadKontrol via USB. Maybe they have Korg drivers built-in? Mac OS is not recognising it as a MIDI device, neither is the OP-Z. Ideas?