Anvils made of ADC (Advanced Diamond Composite) have been introduced for a double-stage multianvil system. Using a hybrid system for the second stage anvils, composed of four ADC and four WC cubes, we were able to produce pressures to 28 GPa and temperatures exceeding 1500°C. In situ X ray diffraction measurements on some minerals have been successfully performed with a combination of the present high pressure system and synchrotron radiation. Only in two runs some failures of ADC anvils have been observed out of more than 10 runs so far conducted using the MAX80 and MAX90 apparatus at the Photon Factory, National Laboratory for High Energy Physics (KEK). The present system may be used on a routine basis for experiments under pressures to 30 GPa, and at temperatures approaching 2000°C within the force capacity of these apparatus.