Alan, I'm sorry to hear that you are being denied enjoyment of plays you want to watch. I have two suggestions:

1. Note the names of the chief actors in the play. Send them a brief letter saying that you'd like to be a fan, but you can't hear them because of the loud music.

Do the same for the writer of the play. That should get them going to bat for themselves (and for you) behind the scenes at the studio.

2. An experiment. Buy some hearing protectors such as factory workers use. They are intended to block the noise of machines while letting speech come through. Much pop music is akin to machine noise, so perhaps they will block the incidental music and allow you to hear dialogue.

I always wear them on long plane rides. They mask engine noise, yet allow me to hear all the annoucements just fine.