Duct Tape's suggestion is likely to put this issue to bed with very little difficulty. It is made to do what you need.

Sure, you could get a 5 watt per channel amp, and connect 330 ohm resistors in series with each output to limit current to the 'phones, and solder up whatever cables and adaptors are needed to get the signal to be right.

But buying the right thing at the outset is the simpler solution, and less expensive of your life energy than doing it yourself.

As for me, I quit making little doodads like this for people because of the inordinate amount of time involved in putting together all the simple little pieces. The time involved in putting it into a case and connecting it to power is more than I wanted to devote to the entire project!