Digital BW, The Print

Jumping in the middle of this not having really read much of the
start...

What about the source image. Was it truly 16 bits per channel? Most
scanners output 12 to 14 bits. Digital cameras output 10 to 12 bits.
They fit them into 16 bit words but the lower bits are all zeroes. If
you start with something like a 10 bit image (even though you are
working in a "16 bit" space), and do some adjustments, especially gamma
related, you are bound to see these bands.

g