Should i get an audio interface?

I have a keytar(Roland AX-EDGE). I play in a metal(thrash) band and i wanna get some heavy tones. I can't make one in this so i thought to take a clean guitar tone and put it through pedals to get the distortion i need. So my roland has a digital out i think. Do I need to get an audio interface or dac or is there any other way. Basically i need a cheap option.