The JBL EON15P are bi-amped/powered speakers, so no need for 'heavy' cables. Any good quality line/microphone cable will work fine.
The inputs on EONs are 'balanced' types, so try to connect them to balanced outputs. (3 wire : hot-cold-shield)

Most of the time jack-connectors cause signaldropouts because the contacts (tip-ring-shield) get dirty. Keep them as clean as possible with e.g. pure alcohol.