Different setup but same situation .If I'm only using one of my JBLs which have a three channel mixer in them I run two cables from the keyboard and plug into two channels on the speaker.
Everything goes thru my keyboard so I don't need to run anything else into the JBL.
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Bill in SC --- Roland BK9 (2) Roland BK7M, Roland PK5 Pedals, Roland FP90, Roland CM30 (2), JBL Eon Ones (2) JBL 610 Monitor, Behringer Sub, EV mics, Apple iPad (2) Behringer DJ mixer