A friend of mine let me have her old Vivitar 2x macro teleconverter, and I have experienced similar limitations. Due to the lack of aperture ring on the DA L kit lenses, there seems to be no way to alter the aperture except using M mode, which causes it to completely stop down, or Av mode, which causes it to go wide open. So far, I've only been able to use it in Av mode hand held, which although makes the image quite soft, seems to me mildly usable as the metering appears to work. In M mode however, the metering appears to be off by a few stops and I can only get results using a tripod and very long exposures.
Strange that yours can't recognize the DA L's at all, but does fine with the sigma?