Guidance on travel from Triberg (Black Forest, Germany) to Brussels (Belgium)

The routes are valid and the DB web site is your best one-stop resource for train schedules across Europe. They do not sell tickets outside Germany, which is why they don't display a price for any trip that has a connection outside their borders. Buy tickets at a train station, instead.

I think that from the black forest I would go to Basle and take a train to Luxembourg. Do stop in Luxembourg for half a day and see the Grund area, and then the philarmonie (for its modern architecture).
In Luxembourg, you may take the train to Liege, a very intersting city and do not miss Curtius Museum and the district of outremeuse with its famous market on.Sundays. Do visit the cathedral and the sculpture of St Barthelemy
massacre(religion war in Europe, middle ages).
On your way to Liege, you may alsi stop and go and see the romantic watefalls ofCoo. You could also visit Durbuy, the smallest city ib Europe - Bastogne,
Another nice area in the region is Spa - which is where spas were invented. Interesting indeed. Dinant and several casles in the area. In Liege, you can take a train to Brussels.

From Luxembourg, you can stop in Namur which is the Capital of the French speaking part of Belgium. There are also several nice museums to visit such as Musee de Croix. Try their Sugar or rice tart.
Do not forget that as of April 2015 Mons is going to be European Capital of Europe and a lot of things will be going on.
Connections frim Antwerp to Amsterdam are very easy. Go on the Belgian railway website: sncb.be
Deutsche Bahn never gives price for international travel, this does not mean that the listed routes are invalid.
When in Germany, just go to any station and do ask.
So you see Brussels is not the only city in Belgium coming fron the Black forest.
Enjoy your holidays.

Thank you Laura & Florence :)
Your advises are greatly appreciated.

Florence: I will relook into my travel plans & see if I can adjust to fit Luxemburg in, because I am meeting my Belgian friend in Ghent & Bruges on the weekend of my Belgium trip.
If I can't fit it in, I will keep this in mind & have it in my next trip from Frankfurt, in May.

The Deutsche Bahn site will usually sell tickets for journeys starting in Germany, within reason. If you can't buy a ticket from Triberg to Brussels it may mean that you're looking for fares too far in advance. DB generally sell tickets from 92 days before the journey date, so try searching for a date in early May and you should be able to see fares.

"they don't display a price for any trip that has a connection outside their borders."

Actually, that is a misconception. The Bahn does sell tickets online for routes with certain connections outside their border. It looks like in the case of Belgium, connections using a national train (IC) within Belgium would be sold online, but not connections using regional trains in Belgium. For instance, for March 12, I see a connection leaving Triberg at 8:14, changing at Offenburg, Mannheim, Köln, and Aachen. From Aachen it goes by regional train across the border to Welkenraedt, Belgium, then by IC from Welkenraedt to Brussels. The Bahn says you can purchase a full fare ticket online for 124,40€. Saving Fare tickets are not available for this route.

One thing you cannot get online is a fare for a connection using Thalys from Köln to Brussels. However, there are Savings Fares for connections using an ICE from Köln to Brussels.

The quickest train route from most of SW Germany to Brussels is to take the ICE from Frankfurt. However, it only runs a few times a day, so you would have to time your ride from Trier carefully.