Dish Network 921 Receiver DVI & Other Related Questions?

[Susan4ET]

Can Dish Network's 921 Dual DVR Receiver DVI connection in the back be
safely used as a DVI input to then offer format control to a monitor that
otherwise does not offer format control? I notice that DVI like S-video
do not mark connections as input or output.

Are there A-B switches for DVI? What is a good cheap but adequate DVI
cable, connector, A-B switch Internet or store front source?

Thanks.