Is there anyway to connect a K8061 interface or a similar device to the Velbus system? I like to measure 8 different water temperatures (maybe even log them) and then use them to control my heating via my velbus system

No, that’s not possible. Kits have nothing to do with our Velbus system.

I’m (still) working on a “plc” program that interfaces with velbus. But since I’m rebuilding my house I didn’t had the time to finish it. At the moment I’ve got a version that works with a k8055 and a 1wire system (very nice to mesure water temperatures etc). This version runs now for almost a year stable (an college of my is using it to control his electric and sun boiler with it). Normally when it’s all become a bit calmer here the program could be finished in a week or 2.
Little remark, the program runs under linux …