Looking for a schematic for a decent headphone amplifier that will run on 5V. It is not going to be USB powered so I can provide up to about 2A of dedicated and fairly clean power.
With that much power a boost converter would allow your +5 volt "limitation" to work with a lot of different amps....
Here's a thread to give you some ideas:
Lots of boost regulators here, some with digital voltage readout:-