Now that you have found the command line, there are 2 final things you could check. If you connect a USB optical drive to the NAS and enter the dmesg command do you see any USB related messages at the end of the output?
For my optical drive the output is:
[ 549.658969] usb 1-2: new high-speed USB device number 3 using xhci_hcd
[ 549.935668] usb 1-2: New USB device found, idVendor=093b, idProduct=0048, bcdDevice= 4.35
[ 549.935675] usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 549.935679] usb 1-2: Product: DVDR PX-755A
[ 549.935683] usb 1-2: Manufacturer: PLEXTOR
[ 550.463094] usb-storage 1-2:1.0: USB Mass Storage device detected
[ 550.463537] scsi host3: usb-storage 1-2:1.0
[ 550.463594] usbcore: registered new interface driver usb-storage
[ 551.469965] scsi 3:0:0:0: CD-ROM PLEXTOR DVDR PX-755A 1.06 PQ: 0 ANSI: 0
[ 551.475036] sr 3:0:0:0: Power-on or device reset occurred
[ 551.479694] sr 3:0:0:0: [sr1] scsi3-mmc drive: 40x/40x writer cd/rw xa/form2 cdda tray
[ 551.497933] sr 3:0:0:0: Attached scsi CD-ROM sr1
The interesting part is the sr1 device, which brings us to the second check. Any output on a ls -l /dev/sr* command or just a “No such file or directory” message?
brw-rw----+ 1 root cdrom 11, 0 jul 30 17:01 /dev/sr0
brw-rw----+ 1 root cdrom 11, 1 jul 30 17:10 /dev/sr1