Steve from Empirical:
Does the Synchro-Mesh improve the optical out of most TVs, especially Sony?
If it's PCM, the answer is yes. If it's Dolby Pro-logic or Dolby Digital, you need the iFi SPDIF iPurifier.
Does the Synchro-Mesh improve the optical out of the Apple AirPort Express (sadly becoming legacy)?
Absolutely. You would go optical into the SM and coax out to the DAC.
Do you know of a high quality AirPlay streamer (source only) that can take the place of, or improve upon, the AirPort Express?
To get a higher quality streamer, you will need to change to DLNA/UPnP renderer like the Empirical Audio Interchange or the Sonos Connect with Synchro-Mesh.
The Interchange will play up to 24/192
The Sonos Connect will play only 44.1
Interchange will deliver 10-12 psec of jitter at all supported sample-rates from these outputs: S/PDIF coax, AES/EBU, I2S SE, differential I2S on HDMI connector.
https://www.audiocircle.com/index.php?topic=156409.0
Steve N.
Empirical Audio