ok. now i understood.If the output of your STB is throwing output of 1080i then whatever you select it will show you same quality if your TV is also supporting the same.
tv is 1080i.
stb is also 1080i. so if i select 576i or 1080 i does not matter bcoz stb is configured like that only.
but it is very strange bcoz hdmi is showing 576i when i select 576i n hdmi is showing 1080i when i m selecting 1080i
so one can get 1080i in 576i also.