On my Marantz SR4300, with "no sub" selected, its only possible to set the rear surrounds to "none" or "small". Apparently if a sub is fitted then you get the option to set them to "large" (I don't have a sub myself). This question was raised by someone else in another forum and it became clear that several SR4300 owners were reporting the same behaviour. No one seems sure if its supposed to be like this or if its a bug/defect. Cheers, Paulus.