Make sure you are exactly following the steps in the manual. If not, you will fail.. I did for 2 internal releases. The manual steps are the only way to take this very complex function and put it in the hands of general users.
Also, try with songs from different CDs and singers. If the vocal has a chorusing effect added, it will create the tunnel echo effect you seem to be hearing. There is no way we are aware of to processing a song with a chorusing effect added in the mix.
If anyone ever developed a product that could take a mix and break it back into the individual sound tracks, I assure you, you could never afford to buy it!
It would be worth a GOLD MINE! 