Digital BW, The Print

I posted a couple of weeks ago regarding previewing in photoshop an 
image to be printed thru OPM. Antonios sent a really great reply, 
very in depth. I thought it might sink in but i still don't get 
it...This morning a new scan adjusted in photoshop 5.0 with a dot 
gain curve that matches a 21 step greyscale thru PZO printed like it 
was expected to thru the PZO export plug.  Saved as a tiff and sent 
thru OPM on the same sheet of paper prints too light compared to the 
monitor and PZO print--I spoke to John at BOWHAUS and I thought he 
said images should print similar to PZO.what do I do? Make new dot 
gain curve for the OPM 21 step greyscale and  adjust the image in 
that situation? G3/OS9.2.2/photoshop 5.0/MIS FS/1280.
Thanks, a thick lurker-jack