Welcome to the nerw vortexbox.org site. You need to register before you can post: click this register link to proceed. To start viewing messages, select the forum that you want to visit from the selection below.
I'm not using Kodi. Do you have details as to the HDMI support needed? My big server for movies is running Vortexbox and the Server came with HDMI Out on the mobo which I am running to an ACER display so I can use the CMD Line. The HDMI is working for this purpose if that helps.
The HDMI card you speak of will essentially be a second video adapter. Probably a low profile PCI card with relatively low GPU capabilities. I'd pick the card that fits, has the best possible GPU, and is supported by standard Linux drivers. I believe the BIOS (Setup) can be configured to disable the onboard graphics adapter. At this point you just need to make sure your add-in card is supported by Linux. There is really nothing special about this. Rack servers have limitations on height, length, and power connectors so a high end graphics adapter may not fit. As a former Dell System Engineer, I can tell you that your desire for a graphics card in a rack server is not unusual.