Hi there did you ever got that fixed by Voda? I have the same issue - the quality of streaming is noticeably lower than what can be achieved over the antenna with TV built-in decoder. more compressed, saturated blacks.
I had the same problem but changed the box resolution to 760p and it improved. On 576p was better than 1080p but 760p the best? Not a tech guy but I found this worked but cant explain why! I tought 1080 would be the best picture??!!