Fred-
Being as no one more technically versed in this technology has taken a stab at your post, I will attempt to help. SDI is a type of video connection that eliminates any digital to analog conversion that regular component and S-video outputs usually have. The point is that the disc video info remains in the digital domain, and can be transmitted digitally to another SDI input. Keeping the info in the digital domian offers a much higher quality picture from your dvd player.
This connection has somehow been omitted from the dvd forum that has agreed to copy protect the current more common connections, albeit even though they are still analog connections.
This mod is usually being coupled for use with a scaler or processor from a company called Vigatec that offers an SDI input to process a pure digital video signal and output it to a conventional display. The processors then transmit in analog to the source, if I understand the scheme correctly, and offer a much improved picture to your display.
I own a Proceed DVD transport and Sony LCD 11HT projector myself, and really don't understand the value of the final analog conversion..... Earlier this year a company in Ireland was reported to have demonstrated, and I was hoping to offer, an SDI DVD player and SDI input LCD or DLP projector.
In short, having the SDI connection on both source and display seems to be the optimum setup.
I really hope someone from Immersive, or otherwise chimes in here to offer you more info. , but that's what I know.
Hope this helps a little,
M