Paul, you have a fabulous scanner !
I believe it has SEIKO software,
If it is like my Epson V370 Photo.
Try copying my settings and give a stamp a go
Do a "preview" which scans the platen
then draw a "carousel" (Marquee) around the stamp at 600dpi
You should have then a blindingly good image around 300Kb
Good luckPS: "Blu tak" a sheet of black paper to the inside lid of the scanner