Bob, the only thing I think you can take issue with . . . .
You're missing the obvious:
Ground loops don't exist until we do something to create them. Until then, there are simply various supply points that
may or
may not have slightly differing potentials relative to each other, or a given earth point.
My loops don't cause trips to GFI outlets or breakers, and they also don't inhibit the safety function of either application of that circuit protection. What they will do is prevent the
creation of a ground loop between two points in a sound or AV system owing to the ground leg of the corresponding power outlets.
This is an infinitely safer practice than cutting the ground lug of power cords, or using adapters with no ground connection (which is probably how 90% of every DJ reading this deals with the issue, including yourself.) It also eliminates the need to lift the ground on balanced audio connections because it prevents the most common source of ground loops - which are those owing to differing AC supply points.
Any DJ who is plagued by venues in their area with these ground loop issues and regularly uses more than one conventional 15/20A outlet at a given site should be using a Hum-X. As we use more devices (TVs, active speakers, etc.) and start linking this outboard powered stuff back to a central rig - we are at risk of creating nuisance ground loops.
I believe you will find in Article 250 of the NEC that you cannot put any device in series with a safety ground. . .
Hopefully that won't be your response to client's when your setup sounds more like an electric razor than music and voice.
GFI is largely not used in theatrical systems because of the extensive use of shared neutrals. GFI breakers and outlets will not tolerate any imbalance in the load. Thus any GFI downstream of the distro is on the legs dropped for clients, vendors, etc. There are differing code sections for consumer, commercial, and theatrical systems.