Need Some Input

So I just picked up a Benjamin NP XL 1500 in .22 and bought the straight shooters pellet pack to find what it likes best but here's my dilemma I already have a sumo from donnyfl and if I take of all the stock shrouds the sumo will screw right on would like to get it quiter if possible. But do I try the pellets with the stock stuff or the sumo or some with stock and some with the sumo. Thanks all