We have received update 7.7.9.
7.7.9 is only for AC units. Extreme and Time Capsule.
The last version for A1264 is 7.6.9
The most recent update for A1392 is 7.8
The only model you can upgrade to airplay 2 is this one.
(A1084 and A1088 are no longer supported in the current airport utility and have not been supported for a long long time.. The last firmware is 6.3 and released in 2006)
Update the firmware on your AirPort base station - Apple Support
And you can see from several posts here it is not without issues.
Problem streaming from iMac to Airport Express after firmware update
Airplay 2 Audio latency adjustment?
This is perhaps the most serious where the Express was bricked by the update.
AirPort Express displaying static amber light
Why isn't music playback in sync between my computer and airport express after installing firmware version 7.8?
7.8 sound glitch
As you can see I have only gone back a couple of days.. this of course happens whenever a firmware is released.. it is good for some terrible for others.. indifferent for most.