I decided to add a remote receiver. This allows the Player to be further from where the controller is used. In my case, the player sits on top of the wall-mounted TV set. The controller is on a table below the TV. Usually, the arrangement works well. But as the battery runs low on the controller, the Player starts missing button presses.

I put the Player circuit board into a small box without the Raspberry Pi. The START and STOP pushbuttons are not used but can be installed to help with mounting the circuit board in a box. Do not install the 10-pin connector. The circuit needs 5 V. My prototype is powered by a 5 V cellphone charger through a USB A cable that is cut to pull out the ground and 5 V power connections. Standard 3.5 mm mono cables are used to connect the remote receiver to the Player. Be sure the left 3.5 mm socket on the remote receiver goes to the left 3.5 mm socket on the Player. Mixing up left and right will confuse the Player. I could not find a source of long 3.5 mm mono cables, so I bought connectors and wire and made my own. 

With long enough wires, I mounted the remote receiver on the back of the table where the controller is used. The short distance from the controller to the remote receiver makes the system reliable until the controller battery is discharged. 

As always, I do not consider the new design or use-case final until it is proven effective over months of use. As of this writing, the prototype has been installed and is in use.