Logitech x-240 Sound System not functioning with MacBook Pro When I plug the Logitech x-240 Sound System into the headphone jack of the MacBook Pro, the external speakers continue to play. No sound is transmitted through the Logitech speakers.

I cannot get the Logitech speakers to appear as a choice for sound output. 

Logitech device does NOT have USB... only a headphone jack.

Do I need an adaptor?
Do you try to watch the content of "Sound" options in "System Preference"? Normally the type of stuff you connect on the jack output can be written on this page.

Do you try to connect another kind of speakers or headphone for trying?