Hi again,
I finally figured out, that /dev/discs is only available when stupid-ftp is enabled in the usb application admin page. If it's not, there's no chance to mount any attached usb file storage device. Is this behavior considered "normal" or is there any chance to disable stupid-ftp? My intention is to get rid of stupid-ftp because I'm using dropbear in combination with a graphical scp client to do file transfer stuff from and to the box...