In Amsterdam Central Station they are now building stuff for passport control, security checks, etc. This is on the east side, around platform 13 or something. I don't think it is all the way at the back (15) but I never bothered to find out. Certainly not a separate terminal.
Another interesting detail. I'm told that the Eurostar uses a train signalling system that is incompatible with the one used on the Dutch railways. Which basically means that they have to lock out the entire section between Amsterdam CS and the start of the HSL just to let one Eurostar go through.