It's true that Sierra had lots of problems, though I still get little pops daisy chaining 2 Quantums in High Sierra 10.13.6. I have them connected via Word Clock, daisy chained with Thunderbolt usinf Apple only Cables and Apple Connector, but still random clicks. I have it set as 48khz and as an aggregate device with the 2nd Quantum having "Drift Correction" checked.
What happens is that Word Clock sync is nev er remembered after being turned off/reboot Mac and I have to physically select it, go into the aggragate settings and uncheck/recheck the "Drift Correction" which sometimes sorts it.
It is a nightmare to be honest as it's every session I have to do it...I didn't have these issues with others and it was me that went through the whole process finding issues with Sierra...
Presonus, what is the correct procedure for hooking up 2 Quantums daisy chained, that works in High Sierra?