I have been managing since with the SD but it is somehow sensitive to the working order. After bootup, the SD is placed and then one can use it. If it is already there while booting, it will usually not work but creates an error. Then it needs to be removed and replaced, then it might work again.
Otherwise, the KC901S seems to work fine. However, sometimes I manage to make it hanging and need to a forced restart. 13 days ago