thanks for the help!
i have some of these transistors from old mice... but the more difficult part for me is to figure out how to merge the signals from the twelve transistors or whatever is used into something that doesn't use up all of arduino's pins. There must be some sort of basic ICs for this task, but i have no idea what to search for exactly... kind of like a 12-way switch, but the other way around?
the print head does pretty much instantly stop when power is turned off, so it should be accurate enough to hit a note clearly when it's stopped at the position hot spots.
The stepper solution has a few disadvantages imho: probably less power and speed, and there is way more math involved, as the program would have to calculate: the distance from current fret to the target fret, where the spacing between frets is not even but decreases towards the bridge. Also there would be no way to detect the actual position of the head, so probably it would offset over time if the math formula did not exactly match the neck proportions... With the DC and pos detection in contrast, the head control program would be pretty simple (again, i guess): "give voltage at suited polarisation until pin n says I".