Yes , you can plug a Mic in to a mac , either via the Mic input jack or a Firewire or USB interface such as the Motu traveler interface or 8pre .
If you run the whole gig via a 828mk11 for instance you can do whole mixes and add effects all real time in applications like Logic pro .
The iDJ should also connect to the Mac via USB so there maybe a problem with the User settings in OSX there may be a corrupted system file stop the units use .
We can create a new user on OSX to see if this helps .
Create a new user account OSX
ok lets make an new user account :-
1 Go to the Apple menu , System preferences
2 Click on "Accounts" pane control panel.
3 Unlock the padlock , use your Account password XXXXX
Disable , auto login in the accounts control panel , to choose a login on restart.
4 Press the + button to make a new user , select an administrator account .
5 Name the account , use a simple password XXXXX create the account .
6 Close the pad lock .
7 Restart and log on to your new account
8 Try all the audio settings you need as before to see if there working .
Once you have done this , shutdown the Mac , and Restart from cold .
Log on as the new user , and test
If this cures the problem then its software or / preference / driver issue and not a hardware problem.
I recommend changing the USB lead you are using for a known working one , and or try a second USB2 port on your Mac , do not connect via keyboard hubs , monitor USB ports or extensions.
You should be able to see your USB audio device in Audio MIDI setup , application from the Mac HD / Applications / Utilities folder. Under the control panel menus Audio Devices : and possibly System profiler under USB devices ,
Also try finding your audio hardware in your applications audio preferences .
Garage band , Logic etc ..
Please boot with the device connected to the Mac for test.
Please let me know if this helps .
Edited by iteachmac on 3/14/2010 at 11:54 PM EST