As you mentioned, another room is the perfect solution. All else will disappoint. However, building a screen of Tandy ( Leather Stores) 'pound o board' is a cheap and very effective solution. The only more effective is lead wall paper, toxic and expensive.
Isolation for tube amps
I've read the some of the threads on isolation platform ideas for amps, but am wondering how one can isolate the amps (and other equipment) from ambient sound pressure? It seems that this would be the most predominant force to isolate? I don't know how anyone would be able to isolate one's components from this force unless the components were in the other room. Any ideas?