ps4 isnt compatible with audio interfaces so that would limit you to some sort of analog audio mixer device. those will be larger framed than the mixamp and may not have a stronger amp. higher quality? perhaps, but that depends on the unit.
why not just hook a stronger amplifier in line with the mixamp? you can always run the mixamp on low volume so distortion shouldnt be too bad then use the new amp to adjust your headphone output volume. not the ideal solution, but the mixamp is a bit of an oddball product