Came here with the same question. Thanks for the answer.
Though I still think it's a pretty crappy solution where I can't go up and down through my presets. The middle button just takes you through them in one direction. I'd love to have the presets viewed on the screen and be able to just look over and see if I have to go up or down through the list to get to the station I want without reaching over and tapping it on the screen. Also, if I tap it on the screen, the preset view goes away. So I can't just easily tap through them - I have to click on "All Presets" again to get back there each time. (Not to mention the minus and plus buttons to view the presets is totally the wrong icons to be using to go through the pages. Swiping doesn't even work.) The up and down button on the back of the steering wheel should be how I cycle through them. Or UConnect should make a setting that allows us to change the functionality of the toggles.
Honestly, not sure who's doing the UX/UI design over at UConnect, but they need some advice and feedback. Sometimes it just feels like a hot mess navigating through those screens - but especially the Sirius XM implementation. Some user testing before designing/releasing this stuff would go a LONG way and improve the experience. I'll gladly volunteer!
