Wen using the ProTools HDX audio interface in ProTools, it becomes unavailable in all other applications. So let's say you want to play audio from youtube while ProTools is open. You can't use the HDX for it. One solution is to use Aux IO, but that leads to inconsistrent results. The other solution is to use a Youtube downloader, which is honestly not a bad solution. But if you really want to play apple music or something else without the inconenvince of closing ProTools,