Had exactly the same problem with B&O blaming Sky and vice versa. Problem solved by replacing the Amstrad with a new Pace box. When I say solved, it was for the vast majority of the time, but when the problem reoccurred I simply switched to TV and then back to Digital, which seemed to cure it
The main problem withe the mark ii is the lack of connections - don't even ask me about my problems trying to connect Beomedia 1 and the Apple TV
In the end, I bit the bullet and bought the mark iv