For Icecast you do need some additional information beside its port, address and password.
In order to be able to connect to your icecast server as a source you need to use the user-name:”source“. (There is no username when you setup a SHOUTcast client.)
Which mountpoint?
Using icecast enables you to use a mountpoint you have to name yourself when you setup your client.
Such as “/listen.mp3″. So your in-game music url was http://jas.slstreaming.de:YOURPORT/listen.mp3 (If jas.slstreaming.de is the address of your mainserver.)
You can even have more than one mountpoint. So you can run more than one stream using a single port on the server.
(There is no mountpoint-setting for SHOUTcast clients.)