JBL GX-A604 Owner's Manual page 7

GX-A604 INPUT CONNECTIONS: 4-CHANNEL OPERATION
Connect your source unit or processor's front and rear left and right outputs to the amplifier's inputs as shown in the illustration.
See Set The Crossover Controls, on page 11, for information about setting the amplifier's controls for 4-channel operation.
To use the speaker-level inputs instead of the line-level inputs, see Using The Speaker-Level Inputs, on page 12.
Source Unit
Front Line Outputs
Rear Line Outputs
7 7
www.jbl.com