I do have the IDC AMEX card since I move around the world frequently. I am originally from Germany and use this card every time I visit home. It is a mag stripe- only card and I have also used it at the Deutsche Bahn automated machine to buy tickets - I did not have an issue at all. Card is accepted and processed without PIN.

Is there maybe a ceiling amount that it allows on those machines? I never had a very expensive ticket, usually around EUR 100 and I never faced any problem charging it to my IDC.

From my point of view, the general card acceptance in countries like Germany is a much bigger problem from my point of view. You always must carry a Visa/MC card as backup. And then you have nice clothing shops like Peek & Cloppenburg that accept AMEX only