Thanks for the reply. First get to the E30 part. Yes the toslink will isolate the thing. And if the pc is isolated like some laptops it's fine too.
You are correct about properly grounded or completely isolated. Yet it's apparent some picture showed the input trace got jumped. But when I measure the metal part on the pot is also not connected to the pins electrically. Well sure the isolation must be poor but you get the idea.
ESD will find its way through the shortest path to the earth right? If you think about it, it takes quite a lot to travel through 1612. Another issue is mentioned by
@solderdude, input resistance is quite low for best noise performance. If I increase the resistance the current may find another way to flow. Hence the second solution I mentioned. Creating a predetermined path for ESD current such that the current won't flow through the components.
The other thing is, if you take things like this out and focus on it, a lot of engineering can be done to it. Were it not for yhe failure, such investigation will not happen.
As a side note, O2, El Amp, El dac series, magni, magnius and a few others all have similar design yet no major issue. I wonder why that's the case.