Ive got a setup with 8 zones of distributed audio from an amplifier, plus 1 zone of optical out from the same amplifier to a soundbar.

The amplifier allows me to set a delay on any / all of the zones inc the optical out zone.

The problem ive got is setting the delay to the correct setting. At the moment ive got all the amplified zones delayed by 20ms, but it still sounds a little off and no matter how i adjust it, its never perfect.

Is there a best practice / workflow for working out the delay ? Ive been trying to do it by ear, and can get it 90% but it always seems a little off ?

The "correct" delay depends on your point of observation.

Sound travels approximately one foot per millisecond. If you are standing next to a speaker and another speaker is 30 feet from you, that speaker will seem delayed by about 30ms. At the same time an observer near the other speaker will claim that your speaker is delayed by 30ms. An observer standing at the mid point will claim that both speakers are aligned.

Thanks @Buzz distance from speakers isnt something i factored in, i was more looking at the delay that Soundbar would create by converting optical LPCM to analog and amplifying it.

We outfitted an outdoor restaurant with a SONOS based system. There was a sound stage about 70 feet from the dining area. Wiring was very difficult. We used a CONNECT to bring an audio feed from the stage to the dining area. Since there is a 70ms latency for Line-In, the alignment between direct and amplified audio was perfect. (This was not something that we discovered after the fact. It was designed in. As soon as we noted the 70 foot dimension, we rejoiced -- otherwise we could have had a nasty timing issue to deal with.)

Whatever you do, charge hourly.

Getting different dacs to time align is a fools errand.

You'll never get it to time-align if you're in one zones and can hear more than one other unless you only want to do that for one zone. Every time you move to another zone, the alignment goes away and the only way to make this a non-issue is to prevent each zone's sound reaching the others.

If you really want to come close, download an oscilloscope app for your phone and record a click track to another source like another phone or a computer. Play the track in both zones and delay the one that's closest- you'll see when they align.

Is the amplified audio, which plays away from the stage, AT ALL audible halfway to the stage, or worse yet, at the stage?

The audio signal going to the dining area is delayed by 70 msec. That matches perfectly with the physical delay of the sound from the stage to the dining area. Now let's say you stand directly in the middle between the two locations. The stage sound will be physically delayed by 35 msec; the dining sound's audio signal will be delayed by 70 msec and another 35 msec in the air, so at that point the dining signal will be 105 msec behind the stage signal. That should be very audible unless the dining area sound is much lower in volume than the stage sound.

As for speaker spacing, the reason that always should be considered is that if you have, say, a 20 msec tme difference between two zones that are 20 feet apart, the electronic delay will only be half of your delay.

This is why background music systems for large rooms use speakers that are not terribly far apart. Those systems are almost universally monaural,* and if you move around in the space, by the time you get from one speaker to another, the speaker you're closest to is enough louder than the next closest one that you hardly notice the delay.

*we recently had a client complain about a design for multiple speakers in a LARGE dining area, them saying "it's not even stereo"! In such a case you have to educate them about stereo not being worthwhile.

Minimally, but there are rarely any guests in that area and the dining area level is not run high enough to be a problem in the mid area or the stage.

The facility is completing its 3rd season and everything has been fine.