Search online for "Classic 47 Headphone" and you will find kit´s to solder that are basically cmoy headphone amplifiers.

As im still waiting for the PCB´s i soldered up such a kit to give it a go:

Both Op Amp´s are already in sockets and its delivered with a set of NE5532.

So far i have given it a quick test to confirm it works, and then tried to hear a difference against OPA604 and AD8065. But i cannot say that its a clear difference...