The one to use is not the 50Kohm - 600ohm version - that's an impedance matching transformer used to drop unbalanced H-Z microphones to Low-Z balanced inputs.
This one:
1:1 600ohm is the one to use on a balanced line to eliminate ground loops without changing it's electrical characteristics.
Any transformer will break the ground loop including a direct box but, you want to match the type of termination to the connection at your destination input/output.