Hi David,
You know me - I don't particularly, usually, like these computerised voices. HOWEVER ... here, you have found something good. This voice sings naturally, and carries the song well.
The song is beautiful! It tells the story well, and yes, I can feel the Carpenters influence, a little, on it - even if you say you turned away from it :-) Yes, there are a few harmony limitations because of the robot voices, but who cares about that.
My only quibble is that the voice currently sounds a little like a boyband voice (Backstreet Boys, Westlife, that kind of thing, haha). If you could somehow make it a little darker in tone, perhaps, more "serious" or something, more earnest (if you like), it would sound even better, perhaps. But what do I know? I enjoyed the song - and yes, the explanations, too :-) - they helped me understand the process behind the song, and that's always a wonderful learning experience, for me.