Hi again,
I'm assuming you have Broadwave relaying the "stereo mix" from your PC, i.e. whatever the PC is playing, so you can link anything, e.g. mics, audio in (using the Line In jack) or any other sound source.
For "any other sound source" you might be using Winamp to play MP3s, for example.
In my case, I relay audio from an external location, and you can use Winamp to listen to that location, just by specifying a URL, the URL for the remote source. These remote sources could also be using Broadwave too.
I use the radio automation program ZaraRadio, which can select a variety of sources, live and pre-recorded, and then use Broadwave to relay the output of ZaraRadio onwards to the transmitter.