Sorry, can't help you on the zumo cable.
I've got a Nuvi 750 on my vtx and bought a 12volt power outlet at the local autoparts store and hardwired it to the battery with the power outlet in the toolbag attached to the handlebars. This allows me to use the power cord that came with the Nuvi while the GPS sit in a Ram mount specific to the 750.
I own Garmins Zumo 550 and Nuvi 880. They are not compatible. If you WOULD however, still like to use your Nuvi on your MC, I have seen Nuvi-specific hardwire kits at either Cyclegadgets or CycoActive online (I don't recall which); or alternatively perhaps Google "nuvi hardwire kits" or similar and see what you come up with.
Lastly, I would wholeheartedly recommend and welcome you to visit and sign up on The Zumo Forums. The only forums created for a single GPS. We now have over 15,000 members since we started in November, 2006 when the Zumo first shipped. Any and all questions not already asked, can be!