OK, once again thanks to Thomas for putting me in the right path to continue with the configuration of X-Surf 100 & Rapid Road.
The X-Surf 100 board and Rapid Road are installed inside the A3000 and I can see a white light coming from Rapid Road.
I have installed Poseidon and launched Prefs/Trident where the status shows as online

Trident - Rapid Road photo 20160322_101129_zpsoj0diav5.jpg
But plugging a USB stick doesn't do anything. I'm reading the instructions in the leaflet that came with Rapid Road but that there's no troubleshoot guide.
Any help will be very welcome. The same to help me to get online with the X-Surf 100.