Playing music to Apple TV & Airport Express - audio sync

Doing searches it seems this might be a long-going problem that Apple has failed to address, hoping someone has found a reasonable solution.

I have an Apple TV (latest gen) and multiple Airport Expresses in my house for multi-room AirPlay audio. Everything works great, and I can play from iTunes to multiple speakers simultaneously. The problem is an audio delay with the Apple TV. I have a room with Apple TV-connected speakers (optical connection to soundbar/sub) in one end, and Airport Express-connected speakers (optical connection to amp/speakers) in the other end. When I'm playing music from iTunes on Mac using AirPlay (multiple rooms), the audio from Apple TV is out of sync, delayed by maybe 100-125ms. This sounds horrible in the open space and makes this multi-speaker setup unusable. When I play to multiple Airport Expresses audio remains perfectly synced and sounds great, this appears an Apple TV specific problem.

The soundbar audio delay / AV sync is set to zero, so that's not the issue. I can't set a delay on my Airport Express-connected speakers, as my amp doesn't have an audio AV sync / delay feature. Everything is up to date, latest versions of OS X, iTunes, Apple TV & Airport Express firmware.

Any thoughts, solutions or workarounds?