[sparqee]

If you aren't worried about the quality of your recording you can of course use your MacMini's audio input.

Another unfortunate issue with using the Mini's native sound card is that you will likely experience a fair amount of playback latency, so if you want to listen to your previously recorded tracks while recording overdubs you'll have to deal with timing lag between what you're hearing and what you're recording (i.e. if you play in time to your previously recorded tracks your overdub recording will not sync up with those tracks). You can always go in and time shift the overdub tracks but it's a tedious way to work. I think most recording enthusiast will agree that a quality audio interface is a necessity.