I have also had trouble with the imic. try goimg direct into the mac. make sur that your mute is off, mon on etc....
this should work. also check your input level in sys prefs.
cheers

Another solution that I just bought and you could purchase and try is the iStudioLink 12ft. instrument cable from Monster Cable ($29.99 US). It is designed to be plugged in directly into your Mac as is supposed to work with any instument or audio device with a 1/4" output jack.
I bough this and the Monster Cable iStudioLink 12ft. mic cable ($29.99 US) so I could use high end mics with XLR connectors to directly record to my Mac. Bought the insrument cable to record directly audio from both keyboard synthesizers and my own electric-acoustic guitar.
These are supposed to work without help of any other needed signal level boost devices and can be plugged directly int the Mac's audio line-in port.

I just purchased these and haven't put them to the test, but the documentation on the backs of these cables says direct plug and play to the Mac from any audio source. XLR mics can use a special electrical step-up transformer adapter that bridges the XLR connection/connector to a 1/4" line that boosts the signal electronically through the cable/adapter without any type of extra special external power boost or phantom power.
Radio Shack sells these.
My guess is with the iLink cables, this step-up transformer adapter is built into the cable itself and is not an add-on other than the 1/8" adapter that is strictly for connection compatibilty to the Mac.