Great question, first off we need to understand the difference between NDI and SDI.
SDI – The SDI Output option converts the output of ProPresenter to a native SDI stream when used with a compatible Blackmagic Decklink Card or UltraStudio 4K product. Meaning you will need and SDI output card such as this. along with one of these at each destination display unless you already have the ability to connect SDI cables to your displays. These devices will convert SDI to HDMI for the display to interpret.
NDI – The NDI output encodes the output of ProPresenter and sends that video stream over Ethernet. Any device that supports NDI input (i.e. PVP, Tricaster, etc.) is then capable of receiving and decoding that video image as in input source. Using a device such as this will decode the output from the Mac Pro to your HDMI displays
If you are able to provide a bit more information regarding how many different displays you would like to drive, we might be able to tailor a better solution. Tell us more about your existing setup, how are the displays currently configured, does each have and HDMI cable running back to a server room, do they currently have cable TV tuners connected to them?