So, I actually put the question to Creative, and they specifically said the headphone output impedance is 2.2 ohms.
Like I said earlier, Texas Instruments recommended a 10 ohm output impedance, but it's not built into the TPA6120A. Creative's engineers must've found another solution instead of a 10 ohm resistor to manage current.
So Whaddya know, it IS MADE FOR ALL YOUR BEAUTIFUL HEADPHONES, haha!
Wait I dont have an X7...... :(