Using foobar has 3 steps involved.
1.) Install foobar on your computer
2.) Add xlobby plugin to foobar install tree directory. ie. C:\Program Files\foobar2000
3.) Add a foobar/winamp zone. You do this in setup (F2). Then select "General" and add the path to foobar exe ie. C:\Program Files\foobar2000\foobar2000.exe
More details are in this thread
http://xlobby.com/forum/viewtopic.php?t=3040
To use winamp you make sure the foobar/winamp zone in the seutp (F2) points to your winamp exe. I have no experience with the 5.1 winamp so I can't comment on it working or not.