Digital BW, The Print

I've mostly been lurking here as I get my digital printing set-up in 
order-and delighted by the information I've picked up.

I recently got a Polaroid SS4000, and have had no problem with their 
software or with Vuescan in scanning BW negatives in grayscale. 
However, in "graduating" to Silverfast 5 Ai, I find that I am getting 
distinct "posterization" of tonalities. I downloaded the current 
version, but no improvement. As Silverfast has innumerable options, I 
may have something set wrong. Anyone with ideas on what might be 
causing this?

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