Headphone connection to preamp or amp...
 

Hi:
Got a set of Koss headphones as a gift. Problem is I do not have headphone jacks in any of my stereo units. Is there a way to build an adapter for the preamplifier rca outputs or my F4 amp. outputs? Is it a matter of just a connection adapter or would a circuit have to be designed? Thank you to all.

Your preamp RCA jacks probably can't work with the low impedance of headphones, and may damage your preamp. Hooking them up to the power amps outputs sounds dangerous.
There is a headphone forum in the"amplifiers" section with many headphone amplifier designs to choose from. I know the O2 is very popular.