jagolevert, local travel authorities don’t publish much info on buses primarily because there are almost no ones. I could only remember Route 395 that may suit your needs. It runs reliably each 2 hours and can bring you from the center of Malmedy directly to Combes/Kemmel or Ster entry (ask driver to stop near chosen one). But you will still need to find a way from Beverce to Malmedy center. When the weather is good it may be a pleasure to walk about 1.5 miles by foot (very beautiful places there, really!), but when the weather is good in Ardennes?:)) Other guests in your or in nearby hotels are likely with a car. Sure they will help you with pleasure.
For local buses timetables you may consult http://www.infotec.be , but don’t expect a lot.:)
What’s your grandstand/GA? Are you going there for all 3 days?