The way I see it. The saxophone player is annoying other people but he is showing his skills to the public. I can tolerate that and let it slip. On the other hand, the boombox jerk is playing music that anyone can privately play. The park is a public space and you should use headphones for that.
When I first moved to NYC I was enchanted and delighted by the various people singing or playing music on the subway but over time it became an annoyance - if I want to listen to music I’ll play it myself.
Please don’t force me to attend your concert by performing in the subway car. I don’t want to be your captive audience. Even more so for people who don’t use headphones.