There have been several discussions of the problems hearing impaired guests have with the Vox units that Tauck uses.
Apple just announced that the new AirPods Pro 2 would have a "hearing aid" function, and that may provide a path to a solution for these guests.
The problem with hearing aids with Bluetooth is that the hearing aids implement "low power" Bluetooth which will not connect to standard Bluetooth. There are small devices that you can plug into a Vox unit which will create a Bluetooth link, but that link is standard Bluetooth, not low power Bluetooth.
The AirPods, however, implement standard Bluetooth. That should give hearing aid users the ability to have a device in their ears that is matched to their hearing loss, and can connect to one of those Bluetooth devices that can be plugged into a Vox unit.
The hearing aid software for the new AirPod will not be out until October. I ordered a set of the new AirPods ($250) and will trial the new Apple hearing aid software when it's released. On my next Tauck tour, I'll use a Bluetooth device on the Vox and attempt to connect it to the new AirPods to see if it will solve this long standing problem.
I'll report the results in a few months.