Digital BW, The Print

>"dither banding" ...lines that
> appear in only certain zones... seems to be related to the dither
algorithms.

Yes. Choosing among the dither options in QTR produces different
effects on different papers. 

QTR's "adaptive floyd steinberg" dither (sheesh...miserable if you
were a kid called "Adaptive Floyd Steinberg" !) works especially well
with alpha-cellulose papers, vanishing micro bands that are evident
with a loupe using other dithers when printing maximum-smooth (eg
grainless medium format out of focus  middle skintones).