Different opamps do not change the sounds of low frequencies. The sub-woofer speaker and its power amplifier affect deep bass sounds. The power amplifier needs to produce high power to make punchy sounds if the sub speaker can produce them.
Subwoofers and amplifier are of good quality. Two 400w 18" and 3000w sterio amplifier. Subs are connected to only one channel of amplifier. my friend have another board. Its output connects to a potentiometer. Input comes to the middle pin and output is taken from pin 1. does this have any impact on sound quality. ( I believe it's not. But I'm really in confusion right now)