Thanks for posting. Welcome to the Community.
I'd like to direct you to this page. It gives you information about the settings options on your remote. In particular, the 2-3-5 option which allows you to choose between different speaker selections.
If you have tried the 2-3-5 option and you are still unable to change over to 5.1, can you please confirm what the sources are that you are watching?
Some of my sources are 2.0 and most are 5.1. It remains on 2.0. I have tried the settings and you say the onscreen menu. Are you talking about the screen on the Bose box or do I need to get it on my TV?? It says speakers >5 with a 3 underneath the 5.
Thanks for getting back in touch.
You can use both to change the setting. It's a matter of pressing the Settings button on the remote, then pressing the source you want to adjust (for example CBL-SAT) then you can choose between the speaker configurations. You can press the down arrow to switch. I would recommend using 5 VIDEO 5 AUDIO.