Problem: 1 PC playing music, 2 PCs in different rooms are desired to play the same track
2018: Solution using mobile phones
I found 3 relevant apps:
- https://soundseeder.com (preferred and successfully set up, after finding a working setting for the delay)
- https://www.ampme.com (3€/week)
2014: Solution using Windows & Winamp
found here: 
- Start shoutcast by going to the "C:\Program Files\SHOUTcast" folder and running "sc_serv.exe".
- Edit the shoutcast configuration file by clicking on "Edit config"
- Edit the parameters in the "Required stuff" section. This includes: MaxUser, Password, PortBase
see  important: set encoder to MP3, 128 kbit
set volume to 0 and usd VLC as client on this machine as well
Media -> Open Network Stream
Advanced: caching -> 10ms