Can't hear my second player... same S bus

I'm new to the Slink-e game, so please bear with me. I have a Sony 300 (master, switch set to CD1) and Sony 250 (switch set to CD1) on two separate S-link ports out of the Slink-e. The audio out of the 250 is connected to the audio in of the 300, and from there the 300 is connected to a single receiver input.

I expected to be able to control everything from CDJ with this setup, and to be able to hear both the output of the 300 directly and the output of the 250 via the 300 to the receiver. Control seems to work fine; CDJ looks like it's controlling things OK and the players are doing what I expected. But, there is no audio when the 250 is playing. Do I need to "tell" the 300 somehow that it should pass through the audio of the 250 out to its output ports?