The US Avant will only accept 480p and 1080i input.  The Apple TV is factory set to 1080P.  The Apple TV owners manual tells how to change its output resolution.

expoman wrote:

The Apple TV owners manual tells how to change its output resolution.

I believe the chang ecame with the latest ATV G2 software update over the network (i.e. an ATV2 out of its box will not have this function, you have to do a software download upgrade)

After the upgrade has taken effect, you go to "SETTINGS" (right side menu) then select "AUDIO & VIDEO" then select "TV RESOLUTION" then select the option you want (I have mine set at Auto)

The US Avant can ACCEPT 480p and 1080i. However, the US Avant can only DISPLAY 480p on its own monitor. The 1080i signal can be forwarded to a connected projector but cannot be displayed on the Avant itself. When you have a projector connected to the Avant, it's ideal to have BOTH a component connection for 1080i and a composite or S connection for the 480i signal. This way, the 1080i signal will go to the projector while the 480i signal is displayed on the Avant. Actually, the 480i signal looks better on the Avant than the 480p signal does because of the excellent video processing the Avant does to the 480i signal, which it does not do to the 480p signal. Also, many of the US Avants are plagued with very bad issues with the component cables. There is often a magenta hue or terrible banding in the picture.

Since the Apple TV does not have a composite or S connection, you have to set the resolution to 480p. You can only use a 1080i resolution through a connected projector. When the Apple TV is cycling through the resolutions to arrive at a compatible resolution, you might have to have the Avant re-detect the resolution by pressing the source button on the beo4 (e.g., "TV" "SAT" "DVD" etc.) in order to see the video.