Question about Miele WWI 800-60 CH

You can use any detergent, even liquid. :)
You just put it in the normal detergent compartments on top, compartment 1 normal, compartment 2 for prewash, compartment 3 fabric softener.

Normal washing powder goes as in any washing machine. Liquid detergent, however, can only be added via the dosing system. However, you are free from the manufacturer and can use any detergent with the help of a refill container.