I'm not sure how Grexx did it with felt, but I believe this is the same concept.

I think this product would accomplish the same thing (dampening the tweeter a bit) although they claim it's used to make the speakers image better.

M60s
VP150
QS8s
Marantz SR6003
Samsung LN52B550
Oppo DV-980H
Insignia NS-WBRDVD