you can play them in either retroarch or with the stock emu. In retroarch I believe you can press select+start to open the quick menu, then there's a setting somewhere for disc control. this let's you select a different disc. As for the stock emu, i'm not sure but I think you just need to place all the disc bin/cues in the same folder, so for ff8 you can create a ff8 folder, put all the bin/cues in there for disc1-4. Then add it to the Games folder. Now when you want to switch discs, you press the "Eject" button