In the manuel is says if you are using a hdmi to connect the sony DAV-HDX285 to your tv you should still use the yellow video cable.why is this?Also I have a vizio vf550xvt tv and i have the optical out of the tv running to the optical in of the tv .Should I run the optical from the hd dvr box to the sony DAV-HDX285 instead and if so why and what setting do I have to change in the tv or cable box.The cable box is a motorola dcx3400.Thanx