attenuation shunt

I read last night about shunting a balanced signal rather than series resistance. What kind of value is best? My output is referenced to +4dbu. Can I use 20k pot straight across hot and cold? I am not worrie about perfect attenuation. more of a utility for when I need to answer phone or for when booting machines. My main concern is whether I can do damage by shunting like that. I asked about 20k because it is the only ganged pot I have on hand
Balanced attenuator

you need an inline resistor on both the hot and cold feeds.
Connect your pot across the downstream ends of the inline resistors. I think they call this a Pi attenuator.
You can design in a fixed amount of cut by selecting either the inline or the bypass values.
You could use a switched attenuator 2 pole 6 way is available as a rotary - straight through & then -6db, -12db, etc... -80db.
Remember to keep the inline values above the minimum resistance required by the source.
If you want constant impedance (seen by the source) I think you may need a 4 pole 3 way giving strt thro' -20db, -40db.
All of these solutions will probably increase the source resistance seen by the receiver so you need to locate the attenuator very close to the receiver.