Your instructions are incomplete.
Assume the incoming message handle is $mh
set ackmh [msgcreate -type reply]
# ADD this statement
msgmetaset $ackmh DRIVERCTL [msgmetaget $mh DRIVERCTL]
The rest of your ACK proc does not change.
FWIW, after adding the above statement, you ACK proc will work just as well for MultiServer and non-MultiServer connections. No need to have a separate proc.
