Thanks for the idea. I am looking for a smaller solution though.
I was thinking of a resistor divider, but I would have to be careful about the "balanced 600-ohm input" to the PA. This may use a centre tapped input transformer to give high common mode rejection of noise (e.g. mains "hum" pickup). If so the centre tap will be connected to ground.
If the output is not floating then I could use a resistive divider/attentuator with one end at ground.
