Balance Audo Circuit

I need help with a circuit design.

I am using RS232 4-wire audio output and need to bridge into another piece of equipment.

I would like to used and build an audio bridge with matching impedance between the input of the bridge in the output of the bridge to other equipment.

The output of the balance circuit would also be 4-wire audio. I need a circuit that will match impedance of 600 ohms both both input & the out put.

I have had trouble finding what size resistors to used in the bridge to match the impedance.

Thanks,

Astro