Wall of Sound

http://en.wikipedia.org/wiki/Wall_of_Sound_(Grateful_Dead)

"The Wall of Sound consisted of eighty-nine 300-watt McIntosh model MC 2300 solid state and three 350-watt McIntosh model MC3500 vacuum tube amplifiers, driving the speakers with a total of 26,400 watts RMS" ... "This system projected high quality playback at six hundred feet with an acceptable sound projected for a quarter mile, at which point wind interference degraded it. The Wall of Sound was the first large scale Line array used in modern sound reinforcement systems, although it was not called a line aray at the time. The Wall of Sound was the perhaps the second-largest* portable sound system ever built (although "portable" is a relative term). The Wall of Sound comprised two stages. One would go ahead to the next city to begin setup as soon as possible while the other was being used; the other would then "leapfrog" to the next show. Four semi-trailers and 21 crew members were required to haul and set up the 75-ton Wall."

Of interest to us bassists:

"Phil Lesh's bass guitar was piped through a quadraphonic encoder that sent a separate signal from each of the four strings to its own channel and set of speakers"

That wikipedia article also contains a clue to why you thought 54000 watts:

"The most powerful concert sound system ever assembled combined the touring systems of Deep Purple, Black Sabbath, Earth Wind and Fire and Black Oak Arkansas, all manufactured by Tycobrahe Sound Co. of Hermosa Beach, CA, plus additional speakers from Phoenix Sound and Flag Systems. Emerson, Lake and Palmer's entire sound system was set up 1/2 mile from the stage and operated with a tape-delay system to match their sound to that emanating from the stage. The total power of the combined systems was reported to be 54,000 watts RMS. The sound was heard over one mile from the stage. The event was called "California Jam," held east of Los Angeles in April 1974. http://www.gambleboards.com/jamtext.htm"