Actually it appears they did create a few cards with hdmi and audi pass-through though as with all of the last AGP cards, drivers are mess. If you do buy one of these cards, download the AGP hotfix drivers from the amd site.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007709+600007850+600031507&QksAutoSuggestion=&ShowDeactivatedMark=False&Configurator=&IsNodeId=1&Subcategory=48&description=&Ntk=&CFG=&SpeTabStoreType=&srchInDesc=
From the looks of it the HIS cards has a jumper on the card to enable and disable hdmi audio pass through. I assume that you want to use the computer as a media center with a tv, so audio pass through is a must.