Your AirPlay speaker greys out because macOS takes it back out of the Multi-Output Device the moment you select that device. You can tick the kitchen HomePod in Audio MIDI Setup, the tick will hold, and then the name goes grey or comes back as Offline Device as soon as the combined one is playing. There is no setting anywhere in macOS that changes this, which is why an hour of hunting through Audio MIDI Setup turns up nothing.
Worth knowing before you spend a second hour: the speaker is fine, the Wi-Fi is fine, and you did the clicks correctly.
Why is my AirPlay speaker greyed out in Audio MIDI Setup?
Because a Multi-Output Device was built for a different kind of speaker than the one in your kitchen. Audio MIDI Setup is a studio tool, and the combined device it makes is meant for hardware wired to your Mac: an audio interface with a pair of monitors on the back of it, everything on one shared clock, every delay fixed and known before a note plays. Ganging those together is easy, because they all keep the same time by design. Apple’s guide to playing audio through multiple devices at once is the official walkthrough, and it never mentions AirPlay.
An AirPlay speaker doesn’t work that way and was never meant to. It sits on your Wi-Fi and settles its timing with your Mac over the network, freshly, as the song goes. That is what lets a HomePod in one room stay with a HomePod in another without a cable between them, and it is exactly the flexibility a Multi-Output Device cannot accommodate. So macOS doesn’t try. It drops the AirPlay speaker out of the combined one rather than keep a speaker it can’t pin to the schedule.
Which means the grey is macOS being consistent, not macOS giving up on you. Annoying, still.
What Offline Device means next to an AirPlay speaker
It means your Mac has no connection to that speaker right now, so there is nothing to combine. An AirPlay speaker only appears in the Audio MIDI Setup list while your Mac is actually connected to it, and selecting the Multi-Output Device ends that connection. The row stays behind with Offline Device written on it.
That produces a loop people go round three or four times before they smell a rat. Pick the HomePod in Control Center, and the speaker reappears in the list, live and tickable. Tick it, select the combined device, and it reads Offline Device again. Nothing in the loop is broken. It’s the same refusal, wearing a label that sounds like a network problem.
Does Drift Correction fix an AirPlay speaker?
No, and it’s the first thing nearly everyone tries, because it’s the one tick box in the window that sounds relevant. Drift Correction, the setting that stops two wired pieces of gear sliding apart, exists for clocks that run at slightly different speeds: your Mac’s own clock and an outboard interface’s, say, a hair apart, one slowly gaining on the other. Drift Correction keeps the slower one honest.
There is no clock to correct here. By the time you would need it, macOS has already removed the AirPlay speaker. Tick it, untick it, tick the other speaker’s box instead, nothing changes, and the reason it changes nothing is that the problem happened one step earlier.
If two speakers you can both hear are drifting apart while they play, that’s a real and separate thing, and why AirPlay speakers go out of sync is the one to read.
What a Multi-Output Device costs you even when it holds
Two things go missing, and they’re worth knowing even if your speakers are the wired kind that stay in.
Your keyboard’s volume keys stop. macOS can’t set the volume of something it assembled out of other speakers, so the keys and the Control Center slider both go dead while the combined device is selected, and you’re back to each speaker’s own buttons. Connecting multiple Bluetooth speakers to a Mac walks through the whole tool step by step and what that feels like in a room.
There’s also no volume per speaker inside it. A Multi-Output Device sends the same sound to everything ticked, at whatever each speaker is already set to, so the bedroom stays loud until you walk in and turn it down by hand. If both your speakers are wired and they live in rooms with a door between them, none of that will bother you much, and the tool is free and already installed. It’s the houses with a speaker you can hear from two rooms at once where it starts to grate.
How to play to several AirPlay speakers without Audio MIDI Setup
The free route is Apple’s Music app and TV app, and it takes about four clicks, which Apple’s AirPlay support note sets out. Both carry their own AirPlay picker with a tick box per speaker and a volume slider under each, which is possible because those two apps talk to your speakers directly instead of asking macOS where its sound should go. If everything you play comes out of Apple Music, you can stop here: how to AirPlay to multiple speakers from a Mac has the clicks.
Outside Music and TV, macOS sends your Mac’s sound to one place at a time, which is the rule underneath the whole business. Spotify, a browser tab, a video call: one speaker each, and picking a second moves the music rather than adding a room.
Audiout is the route that never goes near Audio MIDI Setup. It’s a menu-bar mixer that speaks to your AirPlay, Bluetooth and Chromecast speakers itself, so it isn’t asking macOS to hold a Wi-Fi speaker inside a combined device that was never shaped for one. Every speaker you tick gets its own fader, one Main Audio fader caps the lot, and the volume keys drive that. It’s €24.99 once, and the free 14-day trial of Audiout for Mac has every feature in it. It also sends one app somewhere on its own, so Spotify can play in the kitchen while a call stays where you are, on AirPlay and Bluetooth speakers, which per-app volume on a Mac covers. Chromecast speakers join the house, though not that particular trick.
Can my Mac’s own speakers play along with an AirPlay speaker?
Yes, with one wrinkle that catches people. In Audiout, switch on your first AirPlay speaker and the Mac’s own speakers switch off. That’s deliberate, because sending the music to the kitchen usually means you want it in the kitchen rather than following you around the laptop as well.
The other time, you want both. Switch the Mac’s row back on, and both play. From then on the Mac stays in the mix, and adding the next speaker doesn’t knock it out again. One flick, once, and your laptop stops being a special case.
So: stop re-ticking the box in Audio MIDI Setup, because it will grey out every time and the grey isn’t your fault. Open Music, tick two speakers in its AirPlay picker, and have a listen to what your rooms sound like playing one song together. That’s the thing you were actually after, and it’s four clicks away in the one app that already does it.
Common questions
Why is my AirPlay speaker greyed out in a Multi-Output Device?
Because macOS takes it back out as soon as you select the combined one. A Multi-Output Device is built for speakers wired to your Mac, which all run on shared timing that is known in advance. An AirPlay speaker works its timing out with your Mac over Wi-Fi as it plays, so macOS will not hold it in there. The tick stays. The speaker goes grey.
Why does my AirPlay speaker say Offline Device in Audio MIDI Setup?
It is the same thing under a different label. An AirPlay speaker only shows up in the Audio MIDI Setup list while your Mac has a connection to it, and building it into a Multi-Output Device ends that connection. Reconnect in Control Center and the speaker comes back, until you select the combined one again.
Does Drift Correction make an AirPlay speaker work in a Multi-Output Device?
No. Drift Correction is for wired gear whose clocks run at slightly different speeds, and it nudges one to keep pace with the other. It has nothing to act on once macOS has dropped the AirPlay speaker out of the combined device, so ticking it changes nothing you can hear.