This is very nice!
You obviously have put a lot of work into all aspects of this song.
The virtual voices are quite good, I think. Much better than any i have heard before.
If I may , I would like to make a small suggestion:
When the singer is holding a note, the singer should sing through the note in a dynamic fashion.
A real singer usually would not hold a note at the exact same dynamic throughout a note, but would vary the dynamic slightly as the note progresses. i know it could mean a lot of work for you, but i think would add to the realism a little.
You've really done a great job! i'm really impressed with the quality of your virtual vocalists.
-rob