Does your tech have the ability to post the secondary pattern during the misfire. If not he should, if he can I would like to see the what it looks like.
Both the "pickup sensor" and the amplifier have no reason to cause a single cylinder misfire. It is possible that if the secondary voltage need is higher for one cylinder (due to a lean mixture for example) that a weakened potential caused by either the amp or the coil would not keep up under load.
It is possible that the fuel flow on that cylinder is only enough for low flow conditions.
Bosch Master, ASE Master, L1
33 years MB technician