answer:If you just need extra monitors then you don’t need SLI (or crossfire, AMD’s version). You can just plug any graphics card you like into any compatible slot, connect your monitor to it and off you go. SLI is used when you want to use multiple cards to drive the dispaly on one monitor for example to make games play faster (actually thats probably the only reason). For this you need a comptible motherboard and compatible graphics card that are connected together so that they can share data. It’s a pain to set up and usually not worth the bother unless you have a very hi resolution screen.