Questions
Q1
Why there is no DVI display for my TA790GX A2+ motherboard?

ATI motherboard can only use HDMI or DVI port one at a time.
Because chipset will support one digital and one analog display by design.

Also DVI cannot use adaptor to connect D-Sub monitor.
It need to use monitor or TV with DVI in put cable.
Which means it will only spport digital display for the motherboard's DVI header.