ATI actually said that you can do HDMI via DVI but mind me that would not be the full HDMI, as it would transfer video only.
The HDMI interface has to conduct audio and video signals and therefore you should make a custom graphic card design with an audio connector on the card. It may sound silly but you actually do need this, otherwise you would be stuck with an HDMI graphic card that will transfer video only, not audio.
You also need one more chip - the famous SiI HDMI transmitter chip, which is actually an HDCP content protection chip, to call your computer HDMI compliant.
Although both Nvidia and ATI are only making Media Centre PCs with HDMI compliant cards, we do think that there is a place for an HDMI-compliant card in the super high-end segment. Some ATI partners have just announced that they started shipping X1300 and X1600-based cards with an HDMI connector.
ATI thinks that if you place HDMI connector on the board you have to get rid of the second display DVI connector and this is the trade off that it doesn't want to make. I suggested the chaps use a small daughterboard with HDMI, as we can remember seeing this a few years back with Vivo support. µ
Wiki on HDMI
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