I've used the optical output from an iMac, Apple TV3 and Express to systems in my living room, office and garage. The primary limitation on sound quality in the last two isn't Airplay, it's the high level of jitter inherent in the output from the Apple devices. That doesn't mean you can't enjoy the music, I certainly did in all those systems, but if you want better fidelity reducing the jitter is the place to start.
There are at least a couple of ways to do that, get a DAC (almost certainly a more expensive one) that does a better job of reducing the jitter itself or put a reclocker between the optical output and the DAC.
The Wyred4Sound Remedy Reclocker did a great job in my office system between an iMac and a Simaudio D100 DAC. It made less difference in the living room into a Simaudio D300, a considerably more expensive piece that handled the jitter better on its own.
In the living room I eliminated the Apple TV as an audio source and now use instead an Arcam rPlay. The Airplay signal goes from my iMac to an
Apple Extreme router and then via Ethernet to a Wyred4Sound DAC 1. That made for a substantial improvement.
All this to say that I think your effort should be focused downstream of the Airplay signal.
There are at least a couple of ways to do that, get a DAC (almost certainly a more expensive one) that does a better job of reducing the jitter itself or put a reclocker between the optical output and the DAC.
The Wyred4Sound Remedy Reclocker did a great job in my office system between an iMac and a Simaudio D100 DAC. It made less difference in the living room into a Simaudio D300, a considerably more expensive piece that handled the jitter better on its own.
In the living room I eliminated the Apple TV as an audio source and now use instead an Arcam rPlay. The Airplay signal goes from my iMac to an
Apple Extreme router and then via Ethernet to a Wyred4Sound DAC 1. That made for a substantial improvement.
All this to say that I think your effort should be focused downstream of the Airplay signal.