If you mean physically add it to the receiver, then no, because the receiver doesn't have the processing to do anything with it. There are cheap DACs that will switch optical to stereo analog though.
yeah like john says, it would be like adding a floppy drive to your toaster. Sure, I mean you proparlly physically could, but there't nothing in the toaster that could do anything with a floppy disk drive
I have an older home theatre system that has Dolby 5.1 and an optical output, but no optical input. (I guess they expected you to use the built-in DVD player.) Do you think an optical input could be added in that case?