Here's a simple formula to determine its output power at a given impedance: divide 110 (voltage squared) by the impedance of the headphones (ohms) and your answer will be in watts (110/ohms=W).
So to run through our headphones, the output power of the Deckard into each is thus:
20 ohms (Sine, LCD-X/C): 121/20= 6 W
30 ohms (EL-8): 4 W
70 ohms (LCD-2): 1.73 W
110 ohms (LCD-3): 1.1 W
200 ohms (LCD-4): 600 mW