Just to close off this thread...

Thank you very much to everyone that replied, I tried re-seating and cleaning the contacts of the cards, but unfortunately it didn't help. Therefore, I managed to buy another G68 and have got that working. It seems to have an issue on a couple of the optical digital inputs, but is otherwise fully functional, so I am now very much enjoying setting up, and listening to my Meridian system!

I'm going to keep the 'broken' G68 in case I run into any issues in the future, so that I've got some kind of source of parts.

Many thanks again.

565, DSP5000 (smiley face 96/24), D1500 (96/24)