If you are trying to make "multitracks" from stereo files, do it the same way I make the extras parts for my "Rip" Uploads:
1. Get a lossless version of the song, this is so the parts you try to make won't be screwed up. Import that into Audacity.
2. Find a section of the song that has the part of the song you want to isolate.
3. Find a section of the song that has everything in the last section, but doesn't have the part you want to isolate.
!.This is hard to do, because most songs don't have that. Try using part of an intro if you wish.
!!. Multitracks are in time. So, you'll need to loop them, or do the next few steps A LOT.
4. Invert the part in step 2 with Audacity.
5. Line up the inverted part and the part in step 3 perfectly, so that when you play them you can only hear what isn't in the second section.
6. Select the two and hold Shift then press M. This is the default shortcut to mix the tracks into a new track.
7. Delete everything else, and loop the section to hear it, either by copying it and pasting it at the end of it, or by holding shift and pressing space.
8. This is a section, label it part A or whatever it is called, and export it.
Do this with a LOT of parts in the song, then put them together in order.
Using the Vocal remover and setting it to retain selection will give you some good results, and a lot more to work with if you do it to the whole song, then do the steps above.
Have Fun!
