You did not mention whats your hearing aids modes/maker and whats your Casio piano model.
Please keep in mind that bluetooth have significant latency and you don’t want that when playing piano.
The best solution is the TV streamer connected to the headphone out of your piano, then you are fine because the TV streamer have no significant latency.
See also this tread
Connect the TV-streamer to the 3.5 headphone output of the Piano/keyboard, with the help of an adapter.