those are mixerss for non-amplified analog input sources going to on pair of headphones. if you have high power headphones you would likely still need a decent amp for them post mixer.
the mixamp really is not really the same though. its a combination of decently powerful amplifier, digital to analog converter, surround sound processor, equalizer and basic mixer. it is more akin to a soundcard that has an analog mixer knob added to it given its extra features.
hard to say what will and will not work for your needs given you did not list what your needs were or what products you were trying to use with the devices.