Seanie,
All I can say is when I followed the instructions given in that posting my ATV1 worked on my TV. I got coulour and was able to control it with my Beo4.
However I don't think you can do what you hope with having HD output AND SD at the same time. You need to follow the instructions (and read your TV where this says Avant) and maybe set the Scart input on the TV menu for the correct settings too if required. Other than that I can't help as it worked for me on my BV5 so i don't know what inputs you have and how they can be set, if at all.
Stoobie
1. Use the SCART V-AUX input on the B&O Avant and connect a Scart
to composite adapter (has Scart on one side and three phono sockets on
other (Left & Right Audio & Video)
2. Enable the V-AUX input on the Avant via the set-up menu using your BEO4 and create the V-AUX menu item on the BEO4
3. Connect the three cables between the Scart to Composite adapter on
the Avant to the Apple TV matching the two audio channels (Red &
White) and putting the (Composite) video cable into the Green socket on
the Apple TV.
4. Select V-AUX and you'll now have great sound, but a black and white picture. Now for the spoof...
5. On the AppleTV set the resolution to 480i
6. Now move up one item to 480p, but do not press the select button yet.
7. Unplug the video cable (in the Green socket) and plug in a
(previously bought) HDMI to DVI adapter (£9.99) with a DVI to VGA
adapter on the end (I got the latter with my Mac Mini) You must have
both of these connected to work the spoof.
8. Now press select on AppleTV remote (selecting 480p)
9. Count to 5 slowly
10. Unplug the adapter and plug the composite cable back into the Green socket
11. Wait a few seconds and hey presto colour picture.
Or if you have aTV flash you need to look on their website and do a seacrh on how to install "composited.kext" I think - link here