A little further information to this. I have got the Meridian system to accept my 1TB HDD. The main issue is the drive needs to be formatted Fat32. This isn't a simple process for larger drives and needs to be performed from a command prompt on a Windows system.
Once the drive has the correct format the video files need to be loaded into a folder. It does no let you see files saved to the root directory.

I've managed to get videos to play to the screen but only some of the movies on the drive will play. I haven't worked out yet if it's only DIVX files it's playing.