Basically you could just connect a 75 ohm resistor to each channel, that's a minimal description.
There should be 4 wires on your headphones, 2 of these will be wired to a common ground in your 1/4" plug, the resistors go on the remaining 2, somewhere between the driver and the plug.
These resistors should be just the ticket: http://www.ebay.co.uk/itm/10-x-75-Ohm-0-25w-Metal-Film-1-4w-Resistor-1-75R-/120783575656?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c1f431a68
They have a 1% tolerance, which means they can be out by at most 1% of their value, so each one can measure between 74.25ohm-75.75ohm. You can match them using a multimeter, 10 resistors should be plenty to find a matching pair.
Lyr has plenty of power to drive even the most power hungry headphones, so you could even use higher resistors, feel free to try :)