The 20.7 will absolutely smoke a 3.7i with any amount of subs. properly set up 20.7 do not require a sub. I get great mid and low bass on my 20.7’s after I had them setup by a professional. I had ordered a pair of subs but cancelled them bc I’m getting consistent low 20hz in my room. Fast, accurate bass. I will be having these upgraded to the X version in March.