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).
You also get 20% discount on all Nu-Multi pickups when combined with this set. Use the coupon code NEXUS_SET upon checkout to apply the additional 20% discount on Nu-Multi pickups.
Follow this link for a comprehensive guide: Nexus GK
Pre-order only. Lead-time 3-5 weeks.