K-x and the HD Pentax-DA AF Rear Converter 1.4x AW

According to the spec on the website, the rear converter does not include the K-x as one of its compatible camera bodies, and phoning Ricoh support shed no further light on this topic. Do any members have experience of this combination, say with a DA*300mm or a DA 55-300 zoom?

Thank you much if you can help.