The 4x3 content will have side bars created by the STB if you view it in 4x3 mode on a 16x9 set. You can adjust the side bars in the 2nd settings menu from light to gray, depending on your preference. The HD channel will show the complete 16x9 image, but the local staton has no video for the sides, so it appears black with no video in those areas.
The 8000 should not have passthrough out yet, so output is usually set to fixed, and by default, it is 1080i. If you enabled all the resolutions, you can go into the first settings menu and choose your fixed output resolution. On 720 native DLP sets, ABC, ESPN, and FOX would look best if you change the STB resolution to 720P so it does no conversion. All other channels may look worse at 720P due to the scaling of the box down to that resolution. They should be best viewed at 1080i and the TV can do the scaling. Try it out and compare, but the diferences may be marginal on sets, and dramatic on others.