As for stuffing the cabinet, those foam pieces don’t work at all for mid or low frequencies. For that you want long fibre material. Long-haired sheep’s wool, mineral wool and fibreglass all work for this. The thicker the wad of material, the more effective it will be at absorbing/damping lower and lower frequencies. However, depending on where it’s placed it can slightly or even drastically decreases efficiency when doing a ported box (I haven’t looked at the history of this project yet, sorry about that). I always use damping material for my builds as those resonances can even redistribute through the cone, so it’s actually still a problem for perfectly stiff, sealed cabinets. Only time it isn’t much of a problem is with closed-loop servo subs in a nearly perfectly inert enclosure. How audible these things are is a different matter though, and changes greatly with each project.