What I've always disliked about Thalys is that you cannot buy a connecting ticket from them. Some time ago, I used them to go from Aachen to Amsterdam Schiphol a number of times (usually less expensive and a tiny bit quicker than the ICE via Cologne), and I always had to book two separate tickets Aachen-Brussels and Brussels-Amsterdam.

Is it possible to book such a "through ticket" on any of the mentioned platforms?