No, I haven't tried Plex, although I've read up a little bit about it. I'm coming across a lot of different apps in my research so far, but nothing seems to match the simplicity of Audacity. They all try to do other things rather than just simply stream my collection to my device, as Audacity did flawlessly and rather elegantly (assuming I had a 3g or wifi connection, of course).
I'm looking into uploading my collection (of around 10,000 songs) to Google Play. I guess it's goodin that my stuff will then be stored in the cloud. It can be set up to automatically send new itunes files to the cloud, and you can download files to your device when needed. But my girlfriend and I both have Kindle Fires, and it will involve some kind of workaround to get them to work with Google Play. I know that's not that big a deal, but honestly I have other hobbies and interests to spend my time on rather than spend time screwing around making my smartphone do what I want it to do.