Arylic Up2Stream Amp 2.0 Larger Speaker Cable Connectors

Hi, I have an Up2Stream Amp 2.0 and I managed to fit some of my speaker cable into the stereo +/- L/R audio out (the green looking thing that plugs in) but since it’s so small I could barely get them in and some of them wouldn’t stay put with movement. I was concerned about the wires touching as well. Is there a way to put them in more securely, or a larger, more forgiving plug-in adapter? Do I just need to buy really high AWG cable so it fits, but then I’m more limited on range?