Noise Reduction for AV installation

You may obtain a low enough electrical noise with your existing power distribution. You may not get enough noise immunity with the wrong isolation transformer installed at the correct location. While I have seen a poorly regulated power distribution network damage some under-designed audio equipment, I've never seen power grid noise enter an audio system via the power supply circuitry of the audio equipment. I suppose it could happen. What I have seen though is power grid transient noises entering an audio system through input wire coupling and direct microphone pickup of the sounds from the grid that don't get noticed until review of the recording. A frequent source of this acoustic coupling were earlier use of direct SCR dimmers on some halogen filament lamps on stage. The sharp turn ON frequencies of a dimmed circuit would make a quiet buzz in the filaments themselves on the stage. Often this would be so gradually happening that musicians or actors on stage would not hear this.

But you're in a slightly awkward position here. If you don't install the transformer your AV consultant will blame any noise heard as the lack of this transformer. If you supply a transformer only on the AV consultant's word you might violate building wiring code for your location. Consult with a local electrician if an isolation transformer can be installed in the AV rack itself and if the AV consultant would find that acceptable.