Audio Interface or not

Nope!

A USB MIDI-keyboard or controller works completely independent. The audio interface doesn't matter. That's just for getting sound in and out. Think of your MIDI keyboard as just another input device like a mouse or keyboard.

 

Does the Akai use "real MIDI", that is those two round five pin jacks or does it use USB? If it uses USB then just plug it into the Mac.

But MIDI only send key press information and not audio. Do you want to hear the sound as you play? If so then you need to either play over the Mac's speakers/headphones or use the Mac's audio out jack or buy an audio interface.

MIDI and audio are different things.