The EPI 200 is a great speaker! I Acousti-stuffed mine a year ago or so, but I really can't remember how many bags it took. I think the later ones had the carpet pad-like foam, and the earlier ones fiberglass. I do remember calling PE and asking how much to use....maybe three of the smaller bags? You want to avoid getting anything around the internal air ports on the Passive Radiator.
Early 200 series had a fairly standard "frame with no magnet" passive. The later models have somewhat improved bass because of a specially designed passive radiator that is recognizable by its flat face. It is a very nicely made lightweight "pancake front" moulded unit, with bell openings that were carefully sized to limit the amount of air that enters the assembly. Huw Powell from Human Speakers was telling me that it cost EPI a fortune to develop the ultra specialized moulds to build these. The surrounds on the passive radiator itself are butyl rubber, not foam. Anyway, this is a bit of a late addition to this thread, but I figured the info might be helpful.
** additional info, March 12, 2010: The later models did switch to solid slabs of acoustic foam that line the back, sides, top and bottom. There is nothing on the front panel. There is a wood brace between the 8" woofer and the passive. The passive is a lightweight marvel. With zero modification, these things sound fabulous: deep natural bass extension well down into the thirties. They are bringing out the best in every type of music. Theoretically, it might be good to damp the front panel, but...don't want to mess up something that sounds so sweet!