Basic Music Player with local storage cache and web-based Control Panel

A basic Music Player (Play, Pause, Next and Volume bar) developed in Adobe Flex and its Control Panel in a Web interface (PHP / MySQL). The programming language doesn't need to be necessarily Flex, so I'm willing to hear suggestions about the best language for this kind of software development. The player is a client application and must be installed in a computer. All music files are in MP3 format and will be stored in a ftp server. It's necessary a smart shuffle so the same music doesn't repeat itself in a small amount of time. The software must also have an authentication with login/password, allowing only registered users to manipulate it and it can't be authenticated in multiple machines at the same time. It should have two kinds of users: administrator (myself) and simple user. Inside the web control panel, the simple user should be able to visualize all songs and create new playlists from these, which will be downloaded automatically to the client software. The first 5 GB will be cached so the music keeps playing while the connection is gone and it's important the files inside this cache folder are encrypted (similar to Spotify), not allowing the user to steal the songs, since it deals with copyright. If the administrator removes a song from the control panel, it should be removed from the client's computer too. After installed in the computer, the music player starts to play only after 500 Mb of songs are already downloaded.