The GK-Set is exactly what you need for integrating the Nu-Multi-6 pickup with Roland gear via the 13-pin GK connector. Check out the Nexus GK document for the GK use-case.
This set includes the Nexus Basic ($169.99), 12V Power Supply ($9.99), GK-MIDI Board ($104.99), CV Pot ($14.99), 2-Way switch ($11.99), Multichannel Cable ($84.99), and 19-Pin Output Jack ($24.99).
Please take note that the Nu-multi pickup is not part of the Nexus-GK GK Set.
There are a couple of options to choose from for the Nu-multi pickup.
Pre-order only. Lead-time 3-5 weeks.