DVI vs DSub in SafeMode

What I want to accomplish is for hobby reasons... I know that there are "better" ways to get what I want, but that's simply not my point

I have an old system with an Ati Radeon 7000, when connecting the 'VGA to s-video cable' to the DVI header (via a DVI - DSub converter), booting into SaveMode results in a 'perfect' picture (it's an exact clone from a CRT connected to DSub, only in s-video quality, but is 1:1). After connecting the 'VGA to s-video cable' to the DSub header (and after rebooting in SafeMode) I get no picture at all... I'm confused... Somehow the DVI can "determine" and send a correct signal... I guess?

Because I'd like to connect the VGA to s-video cable to the DSub header some tweaking must be done. I used the Soft-15KHz application to get a picture. It worked, however it was grayish / BW instead of color image and there was some flickering.. So therefore I installed powerstrips because I think it's a matter of adjustments...

Before entering the more advanced tweaking two questions raised:
1. The fact that I get a picture in SafeMode via DVI means that I can replicate it in windows?
2. DVI was able to create a 'perfect' picture in SafeMode, is there some way to interfere what signal was send so I can send the same signal over the DSub header?

Maybe someone can clarify these issues. Thanks,
Dalie