Hi I just wanted to share my opinion.

The Catalyst gives us 2 x 1600x1200 high res RGBHV signal through one DVI-I connector and one Dsub HD15 VGA connector. Theres also a S-Video out for one of the outputs witch will only give you a max res of 1024x768.
This is a much "better" signal than the classic video signal witch only holds 720x576 (PAL and similar for NTSC) divided by two interlaced pictures, based on how the picture is drawn on a TelevisionScreen.

So do we really want to convert the 1600x1200 RGBHV (three colors and two sync signals) to a 720x576 Composit or Y/C (S-Video) or SDI (Digital signal for longer runs than the Composit or Y/C)?

Well yes, sometimes because we want to please.
Apple has made the RGBHV DVI to S-Video interface and sells it for 19US! With this weapon you can supply the VideoWall guys with both outputs in SDI by the relatively cheap S-Video to SDI converter from AJA or other brands.
Remember that most videowalls are low res so you dont even need the 10Bit converter, you could easily settle for the cheaper 8Bit converter.

Just my 5cents
Abbe Westerlundh