You could use an amp with a 3.5mm connection with the DS4, but sound quality might not be as good and you'd have something dangling from the controller. You'd probably want an amp that can use optical, I'm not sure if amps with a USB connection will work. When my PS4 arrives tomorrow, I'll be using the Dr. DAC2 DX TE DAC/AMP combo. It connects via both optical and USB. I'll post again after I test this out. How much are you willing to spend? The Dr Dac2 retails for around $500 at most places (I got mine for about half that price new, luckily), but there are much cheaper alternatives.
Info about my DAC/amp combo:
http://www.headfonia.com/dr-dac2-dx/
Read the OP in the Headphone thread, good info on amps and headphones there:
http://m.neogaf.com/showthread.php?t=417447