I'm not sure if this is a problem or a suggestion, I just know it didn't work

I'm using a MacbookPro (late 2007) OSX 10.7.5 and attempting to combine LineIn with my microphone in order
to play background music to a gaming group while I talk as the moderator/GM.

I've tried following these instructions (http://support.apple.com/kb/ht3956) to create an aggregate device using the Audio Midi Setup of both my internal microphone and Audio Line-in. This appears to work properly because I can see in the Sound System Preferences that I get input from both sources when I choose my Aggregate input.

Over in TS, I create a new playback profile, choose the new Aggregate channel in the drop down list of Capture Devices and try to test it (using TS 3.0.14). I make sure I click 'apply' whenever I make a change. However, I only ever seem to get LineIn and nothing from the microphone. FWIW, All audio channels in the Audio Midi Setup are set to 44.1KHz format. If I choose Internal Microphone in the list of Capture Devices or Built-in Input everything works as expected, but the Aggregate device only takes input from Built-in Input. Am I doing something wrong ?

FWIW, I've also experimented with a USB input speaker in place of the built-in microphone, but the Aggregate device still only takes input from Built-in Input. I've played with Capture Mode settings, too, but no dice.

Any ideas?