Have seen several posts asking about, trying to find out about, ect, and wanted to share our experience this trip.
We took the DB night train from Ams to Poznan, and the train was clean, the room was tight(wouldn't try to store anything bigger than our 2 22" carry-ons, and back-pack). On our train the was no dining car, so if you hadn't eaten, too bad(left at 19:05 from AMS). Take ear plugs if you want to sleep and a cell if you need to arise before the final destination. The WC was down the hall, and the water in the room and in the WC was for hand wash only, not for drinking, however, they did supply 4-1 liter bottles in the room. Absolutely no security issues at all-2 attendants for x number of cars, but no one out walking the hall.
I want to say it worked for us, however, just wanted others to be aware of the conditions, especially if they have visions of a well rested sleep or an amorous adventure with spouse(or significant other). Finally, had several minutes to board and find our car in AMS, but 2 minutes to exit in Poznan.