I´m using StageClix V4 with EMG SA and 89 pickups for about 9 months. It works like a charm without any issue so far. I should mention that the SA are single coil and I have lowered the EMG 89 Humbucker output to match that signal strength. So, maybe my case is not the proof that the EMG Humbucker output can be handled by the V4.
At the time, I was also reluctant to buy because stageclix seems to be a one trick pony company and very small. Thankfully, as I not had any issues, I could not check the service capabilities. Overall, I really like the stageclix and I cross fingers that it will not have any repair needs.