I currently use an Anbernic RG40xxH, but I have a small variety of them to test with. We have a whole thing behind the practice, see https://portmaster.games. I did UFO 50 recently, and I'm still learning some optimization tricks too.
Correct, streamed audio does allow players to access them. If you have a blend of official ost and custom audio, you could go in the middle and have the official ost be streamed from disk.