How are you breaking them up in Acrobat? I suspect if you manually extract pages and save, Acrobat should only optimize the structure and l leave the images alone.
Acrobat might also be combining object to optimize the structure and therefore reducing size. You can check images in the original and the split PDF to see if the compression type has changed, this would be one way to tell if quality is affected.
I like to use pdftk to burst the PDF out into individual pages and then use the same program to concatenate the pages I want back together. This way there is no changes to the objects at all.