I think the general consensus to eliminate the plasticky resonances is to dampen the baffle with blu tack, plasticine, or newplast. Some people have used dynamat but that stuff is sort of a pain in the ass IMO. A newer suggestion is tungsten putty but the consensus seems to be plasticine.
On the cup side the preferred method seems to be paxmate, but felt is a reasonable substitute, and several modders have used fiber fill or cotton too, as a dampener.
Hmm...what about something like fiberglass?
...on second thought maybe that wouldn't be such a great idea.