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I spoke with Rob from Stone Tone about this (I was a little curious, myself) and he told me the story of a concert at which a sound engineer informed him of this difference; unfortunately, the answer is neither detailed nor technical, but anecdotal.
He had just given the Stone Tone Block to the guitarist from Los Lonely Boys, who were opening for Santana that night, and had already sound checked. The guitarist had apparently sound checked with a different guitar, and then for their opening song "Heaven," used the guitar outfitted with the block. The signal from this guitar was so much louder that the sound engineer had to tear the headphones off-- he told both Rob and the guitarist after the show that the level of sound from that guitar (with the same amplifier, settings, etc.) was at the very least 30% stronger.
Sorry the answer isn't more technical than that! The Stone Tone Block's popularity and reputation is largely due to enthusiastic artist endorsement and stories much like this one... I guess hearing is believing!
Hope this info is useful to you, thanks for your patience.
Sincerely,
James McCaffrey
Floyd Rose Support