You need ACR version 7.2 for the RX100:
Only PSE11 can have 7.2, so to be able to use your raw files with PSE9 you should download the free Adobe DNGconverter which can batch convert a whole folder of raw files into the Adobe raw DNG format which your PSE9 can open.
Thanks Michel. It's a pity I have an extra job to process now, but I'm glad I can handle the RAW files in PSE now. The RAW-utility Sony provides is not my peace of cake yet.
Thanks again! Kind regardsd, Leida.