if you get a 3.5mm mic things should be easier for you. you'll be looking for a splitter yes - but a 4pole to 3.5mm 3pole x2 splitter. often you can find them labeled as headset to phone splitters. you still would need the mixamp as an amplifier. it would all need to connect to your controller.
if you wanted handsfree.. its a bit more difficult. for mic the only thing that currently works is a usb adapter for 3.5mm (though you cannot use headphone with this and a mic at same time) for headphones you would need to have an optical to 3.5mm converter. why they do not make things simpler - i have no clue but it is certainly possible to use high end headphones and mics with consoles.