There actually is little to no real difference to the end-user. The reason for the difference is that Technicolor bought Thomson and released a minor update to the DCM475, rebranding it the Technicolor DCM476. Both will work in equal capacity.
Please note: Though they may be similar in appearance and functionality they operate with different firmware versions. They are not interchangeable, if you wish to use one, please ensure it is specifically approved for use in your area.