Okay, not so fun, the KWB shovel that had been working so well broke inside the choke!?
http://i.imgur.com/ov1ONGZ.jpg
It was tricky to get the piece out but finally did. Tried Bosch angled instead and to my surprise, it worked just as well despite the thickness! Let's hope it doesn't break like the one from KWB.
I've now managed almost the entire floor, it's just the parts under the stove and washing machine left. However, we notice that the floor flexes a bit when you walk on it, after all, it's regular particle board. The question is, do we need to use leveling compound? Does it work when the subfloor flexes? Does it perhaps need to be reinforced then? How thick can it become? Also noticing that when you walk on the floor, it can be heard quite clearly down to the basement, probably the plaster and previous casting helped prevent this. Step foam will probably help a little but maybe more is needed? I don't really want to raise the floor as it is already level with the other floors in the house.