Using mzscript (which the theme probably already has loaded), when you press your play/pause button, use this bang instead:

*Script bang !playpause
*Script gotoif ( "%{ampplaying}" = "1" ) pause
*Script exec !Amp_Play
*Script exec !varset ampplaying 1
*Script exit
*Script label pause
*Script exec !Amp_Pause
*Script exec !varset ampplaying 0
*Script ~bang

Note: If you play or pause using winamp itself, the script can lose sync, but a simple toggling of your play/pause button will resync it. So, just don't use winamp itself. :)

edit-

That should also open winamp and start playing it, if it's closed. I'm assuming reluna is using dynamp or geekamp? It's possible they've defined DynAmpPlayPauseNotOpen or PlayNotOpen, which would stop winamp from opening when play is pressed.