Here is my question....when using an epicenter with an active PFM subsonic filter(35hz, 50hz,80hz), should the subsonic filter on the amplifier match the subsonic filter on the epicenter? Should one or the other be set higher/lower than the other? The FS on my sub is 34.89hz. Ported box...12" subs...ft³ a little under recommended for ported. Also....the epicenter has settings on main unit and knob only has one control...do I have to have knob installed? (Soundstream BX-108Z)