Another possible issue: The mimefx.convs rule
application/pdf application/vnd.cups-pdfprintfx 0 pdftopdffxmakes the pdftopdf filter not being used, leading to many CUPS options, like number-up, page-ranges, ... not working any more.
Is this intended, for example because the output of pdftopdf causes problems? Do you resemble the CUPS options in your own pdftopdffx filter?
Perhaps it would be better to use application/vnd.cups-pdf application/vnd.cups-pdfprintfx 0 pdftopdffx Till