This is how it's usually done:
Split your stereo track into two mono ones (Left and Right).
Now, flip the phase on one of the mono tracks - now mix them down into a single *MONO* output (I mean pan them both straight up the middle), and everything that was panned straight up the middle during the song's mixdown will be gone (kick, snare, bass, and Vocals).
It sounds pretty much....like crap afterwards - but that's really how karaoke machines and karaoke software "magically" remove vocals from a stereo audio track. Of course - any vocals that weren't panned straight up the middle will still be there (backup vocals, or reverb/delay on lead vocal).
To compensate afterwards, for there being like....no bass anymore - just EQ some bass into it....or whatever. Play around - good luck!