Got it, thanks.
It's as smooth as silk, I promise. Absolutely no lines at all. If you're seeing lines it must be a problem with your screen, not your file.
Hmmm ... everything seems to be in order there. I can't see why there would be lines.
Did you remember to check the "Dither" box for each of the gradients?
As you said, D&B is really hard in this case. The colour goes all screwy. So instead I used Channel Mixer to make a black-and-white version, THEN did some D&B on top of that. D&B is so much easier in black-and-white.
Download PSD