Thought so! Vocal isolation is mostly a fantasy concept! Vocal isolation is extremely difficult to achieve especially if similar notes or instruments have the same frequency as the vocals. You might have some luck with the VST plugins but don't expect miracles.
This site might help Audacity Forum • View topic - center pan isolation
If you do figure it out, please let me know how you did it! Good Luck.
Eyegor is right. Vocal removal is achieved by inverting the phase of either the L or R track, then mixing to it mono. The out of phase signals cancel, and the vocals remain because they are always mixed in the "center" of the mix. The other instruments are not, they are panned left and right. That's why vocal isolation is so hard, because you can't just do the opposite technique of vocal removal, because there isn't one! Good luck.