The system works by pairing the JBL's Ambient Aware feature to the Vive's Chaperone boundary markers. Basically, when you hit the edge of the Vive activity zone, right when those Chaperone wireframe boundary markers pop up, the JBLs will lower the in-game audio and turn on the headphone's external mics so that you can hear what's going on around you. Move away from the boundary and the in-game audio goes back up while the external mics are cut.
What's especially cool is that this is a software-only upgrade so it'll work with your existing gear when the feature goes live. That said, Harman reps tell me that it's still in beta and they don't have a firm timetable for when it will be released but guestimate that it could be around the end of the year.
I had the opportunity to try out the feature on Monday at the TechCrunch Disrupt conference and was really impressed by it. It's super helpful. Used along with the Chaperone wireframe visuals of people standing near me, I was able to carry on a naturally paced conversation with the Harman rep while wearing both the Vive headset and the headphones. All I had to do was stick my head out of the virtual "room" and I was (nearly) back in regular reality. It's a head-slappingly simple solution to VR's issue of situational awareness.