If you haven't tried setting your box to AUTO resolution then give it a try. In my case with a Panasonic PHD8 via component it improves standard definition picture sharpness since the box doesn't upscale from 576 to 1080i.
When set to AUTO, compare the sharpness of the 'now and next bar' on an SD channel to a HD channel to see the difference.
When set to AUTO, compare the sharpness of the 'now and next bar' on an SD channel to a HD channel to see the difference.