As an application developer, when you play audio, you have to use a device URI. Instead of using the default one, guessing one by listing them or even hardcoding it, you should call ahl-4a/[role] with open as action.
The role to open should be defined in a configuration file or hardcoded. If you hardcode it, please consider to at least define it at one known place so that it can be easily changed.
As opening a role may fail, you should test if it returns a success and a device URI. Both of them should be tested because it’s perfectly fine to have a role without a device URI from 4a point of view (no device is bound to the role thus no audio can be played in this case).
Once you have finished to play audio, you should call ahl-4a/[role] with close as action. This is important to allow other applications to use the role when you are not using it.
You may also want to handle events of the window manager to know if you application is displayed or not, and open/close accordingly the role you are using.