Best filler for speaker stands?

3/8" and finer gravel (till powder size) from a rock crushing plant will work, this is used in hot mix plants for tar roads.
Chopped tires, car carpets, high density mattress foam, car boot lining, the EVA sheets for shoe insoles, they all work too.
 
The better FR88eX has a coloured top, i expect the dirt cheap FE85 version is not as good as it is (FR88 does not stand up against the FF85wk or Alpair 5.2/3).

You are applying your experience wirh a $15 cheapie as representitive of all FRs. Like saying you only need to spend $5 on a tweeter, because why spend more?

dave