Can you explain the differences between your configuration and eBox one? Maybe it help us to find out ebox-printers problems
Following VaineDragon suggestion I tried to create a new printer using Cups web interface and I realize that the Cups wizard show some printer DeviceURI that doesn't appear in EBox wizard.
So in /etc/cups/printers.conf I had replace EBox DeviceURI:
DeviceURI usb:/dev/usb/lp0
with Cups DeviceURI:
DeviceURI usb://HP/Deskjet%209800?serial=MY75O2Z0PH046K
and than the printer work correctly.
Now the problem is: if I restart the server, EBox overwrite printers.conf file.