HK Connect

Fiddly, but works. With my Samsung Galaxy S9, got the hang of it. The instructions are minimal, but I got stereo working on my two Harmon Kardon Onyx 4 speakers (the app only works for Onyx 4). Connect both speakers via the phone's Bluetooth, then open the app. Press the link button on both speakers at the same time, then tap the same icon in the app and choose stereo. You're all set.

Inconsistent connections to my HK Studio 4's. When it does,it struggles to find more than one speaker (both speakers are within 5ft of phone). When it does connect to both (rare), and I can put in stereo mode, it's awesome. I wish the connections were more consistent. The app just hangs on "Discovering."

if you have invested in the HK's, cut your losses and go to Sonos. the app is beyond worthless as well. Speakers don't stay on, even when plugged in, so EVERY TIME you want to turn on some tunes, you need to re-power each speaker..., and then do the HK connect dance with each one, which has zero consistency to which variation of connection methods work.