I saw the Ray Brown Tribute here in Santa Cruz at Kuumbwa on Monday night, alas no John Clayton. It looked to me like CMcB was "using" an AMT, but also had a realist on the bass. I didn't see if he was using an amp or not, the room is small and the PA is really good, so maybe straight to the house?... really though, who cares what he was using, he can play!!
"...sounds like a goddamn train wreck!"