Check it out.
Some users are reporting the controls in the Alexa app are available but the various Echo hardware is yet to receive update. This will be a fantastic feature upgrade when it is fully unlocked for use. (Finally Amazon! 
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Donât forget to like the post
Back in March. Nothing came from it.
Probably because it was a story based on a Reddit post that turned out to be a false claim, complete with a faked screen shot of the Alexa app.
I believe it when I see it on one of the fake news outletsâŚ
I have seen with my own eyes routines appearing in the Alexa app in December 2015, still waiting for Amazon to releaseâŚ
The singularity is upon us. An Alexa can finally control another Alexa (at least for music). And they can be grouped together in different groups for whole home audio. Wha? Check the app! And name your Alexas simple single-word names under settings in the app for easier invocation. âAlexa play Rolling Stones in/on the kitchenâ
Unfortunately Amazon allows âonâ or âinâ but who cares both work!
I Just tested this and it worksâŚ
Big issue for me is out of the 14 Alexa devices I have capable of playing music, 10 of them are connected to Bluetooth speakers. When engaging the MRA feature, it disables the Bluetooth. Iâm left with the audio coming from the tiny Dot speakers.
Could use the aux jack but then that forces a speaker to be on in order to hear the Dot if just asking the weatherâŚ
We typically only turn on the Bluetooth unless we are playing music from a selected Dot.
Yeesh
Wow that sounds like a Bluetooth transmitter (connected to the echo dot aux
jack) is in order. I suspect the reason Alexa WHA doesnât support
Bluetooth is the widely variable Bluetooth latency. Maybe Amazon will
support aptx-LL (low latency) Bluetooth at some point and then allow it for
WHA. But the Show doesnât even have an audio jackâŚin a world where we
need OPTICAL out (which works to 30m now).
I donât see any settings for this in the Alexa app. Is there anything I need to do? What do I say to play the same music on multiple devices?
Make sure you have the newest Alexa app. In settings there is a multi-room music selection underneath your list of devices. The next page will allow you to create a group and name it what you would like. 3 of my devices need a firmware update yet, so I was only able to group the others.
Assuming you have the latest release of the appâŚgo to âSettingsâ->âMulti-Room Musicâ and create a named group. This will enable the feature.
Well, thatâs it for my Google Homes. This was the nail in the proverbial coffin for them. I was only keeping them around for music and now thatâs been covered by Amazon.
That was it. Thank you for that, my iPhone is supposed to automatically download updates but for whatever reason it hasnât in the last week and I just updated it and its there. Thank you and sorry for the silly question.
This is awesome and something I have been wanting for years.
Also, just to make sure everyone knows, this doesnât work with the Tap and I havenât seen anything (so far) from Amazon that they plan to enable it to work with the Taps.
Hopefully, they extend it to them sometime soon.
Have anything in mind? I was hoping that since you could toggle between Bluetooth and Aux that you could also toggle between internal speaker and Aux.
I guess it would be easy enough to just keep the cable unplugged until you wanted to listen on the Bluetooth speaker but my goal is to be as hands off as possible.
A couple of my sound bars can wake up from opticalâŚMaybe an analog to optical device could work.
The last thing I want to do is have something on, using unecessay energy, if I donât need to. All of my sound bars have Bluetooth standby.
I sure hope so too!
I hope there isnât a technical hardware limitationâŚ
Keeping audio synchronized on multiple playback devices is a technical challenge that, perhap (?) Amazon has solved using the far-field recognition built into the Echoâs and Dotâs, but doesnât exist in the Tap.
Then again, who knows what other hardware differences there are in the Tap ⌠maybe someone has done a teardown?
Edit: So Multi-Room Audio seems to make use Bluetooth, eh?
Tap was designed from the start to be more of a âbluetooth playerâ than an Echo, so maybe thatâs the technical challenge ⌠different Bluetooth chipset?
Honestly, I donât think there really is much different in the Tap from the actual Echo aside from a battery and perhaps fewer microphones. As for a tear down:
Well crap, I was all excited for this and now Iâm not. I have my Echoâs connected to Bluetooth and use it for music like you, Otherwise they are disconnected and sound comes out of the built in speakers. Effectively no gain for me. Still in the same boat.
Hopefully some affordable Alexa enabled speakers with this capability baked in will come soon.
Possibly I can relocate some things and plug my speakers in directly? Hmmmmmm
Not into the Echos. Only the Dots have an AUX out. 
I donât think the fact that BT is disabled while this feature is being used is adequate evidence for the conclusion that BT is the means by which the feature is implemented.