Most people doesn’t have latency problems with zynthian, but this is something very subjective and sometimes totally non rational. For instance, some time ago i had a discussion with a keyboard player that complained about latency. BTW, he was not a zynthian user 
I tried to explain to him that he should consider placing the monitor closer to him. The monitor was placed more than 3 meters from his head. I mean:
d = v * t => t = d / v = 3 m / 300m/s = 10 ms
by having the monitor at 3 meters, he was adding 10 ms of extra latency. My moving the monitor to a closer position, he could gain 5-6 ms of REAL latency.
He told me that this was not the problem, that he meant the “delay when playing a note”. “OK”, i said 
The best!