Long cable run: Jack, rca, xlr?

Not, a guitar amp (sorry!), but I know there are some very knowledgeable people here.
This is for a project I'm doing for a friends restaurant: His sound system consists of about half a dozen powered speakers hooked up in corners inside, as well as one for the outside terrace. He's asked me to add another speaker for a smaller terrace about 10m away.
The easiest thing will probably be to daisy chain another powered speaker to the one that is already outdoors. The speaker that's already in place has jack inputs and outputs, so I'll probably have to use a long jack cable.

My question: the cable will have to be about 20m (60') long, will the signal still be ok with an unbalanced jack cable? Or should I add a small DI box and run an xlr cable? Also: any advantage to using rca connectors?

Thanks a bunch!

The only problem with unbalanced would be noise pickup and that is situation specific. RCA's are cheaper and are the standard unbalanced connector for this application. XLR's are the standard for balanced connections and are more rugged and reliable. If you can get away with unbalanced RCA it us usually much less expensive. I think I would take my que from what is used for the other speakers