if Baker Bigsby worked on 4 of his Quad albums , maybe it turned Stevie a little sour on the whole thingi haven't got a Cluemountain was just saying that his Surround mixing goes way back to the Quad days.
as for the Stevie story, it does feel unlikely that something would get mixed in Surround when Quad was to all intents and purposes done for and what we know as 5.1 wasn't even so much as a twinkle in the milkman's eye!