In theory the chances of units' sounding different from each other are no-greater than they are for (these are all hardware, obviously) ROMplers, analogue-modelling synths, samplers, FX units and so on.
In 30 years of buying digital hardware of all the above flavours, I've not once encountered even a hint from my gear or anyone else's that a unit differed from others of the same model sound-wise.
I mentioned output caps in another thread recently with regard to possible differences 'cause I've seen it manifest on old ROMplers, but even then, only when the units have been left powered up for extended periods and allowed to generate lots of heat or run in overly-hot environments... for extended periods. We're talking about units 20 to 30 years old here. The resulting sound was thinner and harsher in all cases; apparently the caps "dried out".