Both speaker upgrades I bought for STTNG in ~2003 or 4 and LOTR I bought in 2005 had these included. One actually had paper wrapped in a circle for RF interference I think too. It's just how it was done before they figured out how to plug in and use the dial included now.
Both upgrades were bought on ebay from pinball pro, dunno if its the same pinball pro but that was the name on ebay at the time.