Vocal removers usually work with stereo material only. They reverse the phase of one channel and remix to mono.
This causes anything that had equal signal in both channels to cancel out.
 
More sophisticated versions allow you to bypass bass, because bass is usually also mixed to the middle.
 
There is also clever software that manipulates percussive instruments. It works by assuming all frequencies that have the same or similar loudness envelope must belong to the same instrument.
 
Melodyne can separate out notes of a chord played by the same instrument.

I guess theoritically it is possible, but in reality it's not practical.
 
An FFT analysis on the tracks would give you everything split up into individual sine waves. Theoretically, you could then choose which sine waves to put back in to the reverse FFT for each instrument and (assuming you've identified the right ones), repeat the process to give you separate tracks.
 
But you're talking of 100's if not 1000's of sine waves, PLUS the transients. So I doubt even if you could identify the right sine waves for each instrument, that the resultant tracks would be of decent quality.
 
The best you could hope for would be to maybe change the balance of each parts, but it would take you forever to get to that stage.

I doubt you'll be able to clearly separate the instruments.
What MIGHT help is putting harsh EQ settings.  For the bassist, roll off the treble and boost the bass.  For the guitars, cut off the high and low end.  etc.  Find the general frequency range for each instrument you want to identify, and make a separate WAV/MP3 for each range.
I expect that's the best you'll get.

I had once the same question, because I wanted to separate the drum instruments of my old recordings, i.e. I had only a stereo track for the drums.
With some search on the internet I found a very cool FREE tool:
ISSE -  interactive sound source separation editor
 
It is not 100% perfect, but with some work you can really separate sound sources contained in a stereo wave file. You have to cut out one instrument after the other from the remaining audio. ISSE is very amazing and free! Have a look!
 
P.S.: By the way I have also tried with the Melodyne Editor. They make a lot of advertising about their separation and this software is not cheap, but it cannot really separate different instruments! Not even the kick or snare can be separated on a stereo drum track. I was really disappointed!
The only thing that I could do with it was to separate to choir voices that I had in a mono track.