Thanks, Alan! But hope is by no means lost.
First, I would give it a try anyway. It can’t hurt to try, and it’s always possible that the person was either misinformed or misunderstood the question. And in fact the manual says that activating mute "will silence the preamplifier main outputs," without mentioning the EPL outputs. Perhaps what the person was thinking is that the mute function would mute signals that would otherwise be supplied to the pre-outs in response to signals received from the EPL **inputs**.
But if the CJ person was correct, I’m quite confident that the following alternative will work: Connect the EPL1 outputs (left and right) to the inputs of the headphone amp (left and right). Select the source you want to listen to. Using the EPL/Thtr button select EPL. Turn the volume control on the CA200 all the way down (although that may not be necessary). Do NOT select "Mute." That should do it!
If by any chance a little bit of low level sound is still heard from the speakers, do everything as above except try selecting Thtr rather than EPL.
Good luck. Best regards,
-- Al