As a rule of thumb, most speakers sound better with the grills off. I have the optional grills for my Magico S5's & found this to be the case. However bare in mind some speakers have been designed such that the speaker grills are an integral part of the design. Two such examples would be the classic Infinity Renaissance series speakers & most of the current Avalon models. Ultimately you'd have to a-b test the speakers with and without the grills to know for sure.
