I haven’t played the Dreamcast since they were an active system, but if you already have the cables to get S-video into your monitor you’re probably fine with that. Technically component would be better, but I don’t know how noticeable the improvement would be. The main improvement would be in color, but S-video wasn’t bad. I would have to doublecheck if S-video supports progressive scan, but if you’re at SD resolution on a CRT I wouldn’t expect you to notice a difference between interlaced or progressive video. Interlaced video was made for CRTs and wasn’t actually bad there, never mind how we appreciate and prefer progressive video on modern flat screens.