The Parcel media stream is shared by all on the parcel and cannot be changed but you can turn it off and switch to the internet streaming radio available in each unit.
All scenes come equipped with a radio which uses 'Media on a Prim' technology to stream Internet radio to your computer. Click the Radio Frame then the Screen to get a playlist.
If you see something like this...
... you probably have Flash installed on your computer. Un-install it from your computer (not just disable it in your browser) and the Radio should work. And by the way, you don't need Adobe Flash on your computer anymore as Adobe is abandoning it. Read this:
You Really Shouldn't Be Running Flash Anymore
The standard parcel audio stream will be fixed to a commercial free ambient music station.
When using the Radio, turn off the parcel audio stream and make sure your 'Media' volume is up.
Go into Firestorm Preferences and check these settings.
Note: Media Source volume rolloff distance is not easily accesible in the standard SL viewer unless you go into Debug Settings from the Advanced Menu (CTRL-ALT-D) and set MediaRollOff parameters, so sound will fade pretty quickly as you move away from the radio.
Most every skybox scene comes equipped with a Television which also uses Media on a Prim. If you don't have media 'auto-play' set in your preferences, just click anywhere on the screen and you will be directed to the Bing home page. From there, it works just like a browser and you can type any URL into the address bar and even click links on the screen. To get a menu of pre-selected stations, click on the TV Frame that surrounds the screen (the TV must already be on for the menu selections to load URLs).