minipac interfaces 2 players with 8 buttons each, and a trackball and spinner all at the same time. the ipac just dows the two player bit...also, i'm a bit rusty on all this, so you'd have to double check with ultimarc for the actual number of inputs. but the key difference is the trackball interface and spinner interface without having to buy an optipac. also, they are smaller and cheaper. lastly, right now the minipacs are all the same, so if you want the wiring harness, which i would recomend for a newb, it's gonna be 69 bucks plus shipping, but if you think you can handle the wiring, you can get the 39 dollar one without the wiring. good luck.