DrakeOldham That info definitely helps. Thank you.
The main issue right now is the 2012 Mac Pro. Apple considers any hardware older than 7 years to be completely obsolete, so they don't support the hardware or the operating system on it any longer.
Therefore, if you want to move to ProPresenter 7 (a good idea if it's in the budget) then I would suggest planning on a computer upgrade. With your current situation, you could probably get by with a Mac Mini and an external PCI chassis with a Decklink card - assuming all 3 of your projectors and the Echolab get the same image, of course. Although I would recommend at least a mid-spec iMac or a new Mac Pro if at all possible.
Is a computer upgrade something you're hoping to do or are you trying to get this done as cheaply and efficiently as possible?