Since when has a trade secret (if there is any involved, I doubt it) become more important than the citizens' right to a transparent election process?
After a quick read through the respective laws such as the Election Verification Act (Wahlprüfungsgesetz) and the Federal Election Act (Bundeswahlordnung), there is not a single mention of any kind of electronic voting machines. To the opposite, they go into every tiny detail of how the ballots have to be formatted, what color of paper they are printed on, etc.
Apparently there is already at least one person who wants to challenge the election results in those counties where electronic voting machines are used. I'm more than motivated to join such action and/or start an initiative for transparency of electronic voting. Stay tuned.