I do playbacks from the original studio versions, it isn't MIDI or similars.
This is a complex process, which varies from one song to another. Do not automatically come as some programs promise.
And it isn't always possible to remove the main voice completely, sometimes remain the effects of echo / reverb added in studio.
I'm a freelancer in oDesk, e-Lance, Guru etc. There is a portfolio with some sample songs.
If you want you can order, and I send a preview of your request. If you approve you receive your playback.