Webpress Vs Digital Book Printing Problem

It's time for the 4th run of my photo story book. It was created using MS Word and converted to a PDF. The first 3 runs were on a digital press but that costs 4 times as much as a longer run of a 1000 or more books on a webpress. My problem is, in the soft proof all the photos are washed out. We are on our 4th try with modifying the photos using photoshop. Any idea where I am going wrong?