Using Thevenin equivalent to find Ix
The thevenin equivalent voltage shows the open clamp voltage between A and B.
During the calculations your resistor was already connected, you shouldn't use the equivalent resistance, but simply the resistor between A and B. 
You just want to know the current trough a resistor with a known voltage over it. 

$$I = \frac{V}{R} \text{ where } R = 6Ω$$

Asuming the 6Ω resistor is part of the circuit your other calculations seem to be correct indeed.