You can locate the BCD3000 control panel in the System Tray of the computer. The System Tray is located on the lower right corner of the screen. It is a black box with 2 grey circles inside. Double click this icon and the Control Panel will appear. You will want to locate the "In A (Ch 1-2)" section of the panel. From here you will want to select "Mic." This will utilize the Mic input on the back of the BCD3000.
To get the mic to work with the BCD3000 on a Mac, all you really need is something that can send a MIDI PROGRAM CHANGE command to the BCD3000.
PROGRAM CHANGE 0 Phono A IN
PROGRAM CHANGE 1 Mic IN
So, to make the mic work, you will need to send a midi program change command with the value of 1.
This is actually easier than it sounds. All you need is any program that records and plays back midi. (MIDI PIPE, Ableton, Cubase, Etc...)
Here is the link to MIDIPIPE.
Here is the download link. (It's free!)
You would first, with everything connected and on record a program change of 1. Save this as a file.
Now, whenever you start up your system (Mac and BCD3000) you would first start up the midi recording program.
Open the file with the program change.
Close the midi recording program, then start Traktor, you are ready to go!