I would also be surprised if it does any processing, but it's good to have a second opinion - the Meridian documentation, at least on this product, is pretty vague.

I'm not using any of the analogue inputs at all, so I'm not worried about that.

I'll try some better cables, and one of my audiophile friends has volunteered to come and help with some blind testing in a couple of weeks time, so this should help to eliminate some of the other possibilities.