I'm completely unfamiliar with the OrangePC series of cards, what i/o does your card have?
Serial and/or parallel? You can easily transfer files that way with the appropriate cable from another pc.
Some have a pcmcia slot, right?
Using a passive compact flash adapter and cheap CF card is a good option.
I saw an ISA slot on the first page, you could also put a network card in there, or a scsi controller.
Can you transfer files from the Mac side to the OrangePc side directly?