Can't OCR old faded typewriter text

I've got reams of documents to put into digital form. I'm using a
Visioneer 9020 and Omnipage 12. 

The original documents were typed on white paper with a typewriter and
probably a worn ribbon.  The characters are light, but quite legible
and very easy to read by eyesight... more of a gray.

But Scan Manager pro will not define the characters. I end up with
about 80% errors. I can't reduce brightness finely enough before it
completely blacks out the preview.

When I set it to automatic, I get no text at all, just a white page.

I've tried several things. Putting a black sheet of paper on top of
the sheet to be scanned, which helped a little.

I've used the grayscale and color settings too so that I could adjust
the brightness/contrast but that hardly helped.

Any ideas? Would photocopying the originals on a good copier transform
the grays into blacks that Scanmanager can then more easily read.

I'm really dissappointed that this sacnner and very expensive software
cannot do the job!

Thanks.