Hi,
I already posted the answer to you in a private message. But since it took me ages to figure this one out, no thanks to the internet, it can't hurt to post the answer here for others to find.
You can't assign an audio source to one of the hdmi inputs. However you can assign an HDMI video input to one of the other predefined inputs (DVD, DVR etc.). For this to work you have to turn off Kuro Link (which is turned on by default). Hook up the sound to one of the other inputs (DVD, DVR, MULTI CH). In my case I use DVR. Then go to the input setup menu and select the input you hooked up your sound to. Under HDMI Input select the HDMI signal you hooked up your macbook to, e.g. hdmi-1 (this option was greyed out before because Kuro Link was turned on). Exit the menu and test. If you still don't get any sound at this stage you might have to use the SIGNAL SEL button on the remote to select ANALOG ( see p. 57 of the manual).
Hope this helps.
P.S.:
AUX, CD and CD-R cannot be used for this purpose. Not sure about BD. I think it has to be DVD, DVR or MULTI CH IN.
If you actually need Kuro Link then you're somewhat screwed. You would have to perform the above steps everytime you want to hook up your laptop/macbook and turn on Kuro Link again when your done with your computer.