Using these methods I was able to get to 22ppb in the can measured via a Hach orbisphere
I beat the brewery testing by quite a bit. 
Looks like you have your process down! I might have to grab a bench capper and hook up my beer gun to set up bottling in a similar fashion.
Given that the cans are sitting sanitized and exposed to oxygen, do you feel like preboiling and sulfiting your sanitizer is a meaningful reduction to TPO? With an automated brewing setup this isn’t as much of a hassle, but it is an extra step. Are you mixing your sanitizer in the water after boiling?