Yes, use loopback. Just pick a pair of unused channels (input and output should both be unused). If Camtasia lets you pick the input, that's great, usually you can only use the first or first pair of channels.

So let's use the AES I/O for this example. Select the AES output pair in the bottom row, click the wrench and activate Loopback. Leave this AES submix selected - you can tell it's selected when the channel strip is lighter gray then the others. Then route the playback channels from software to AES Out (middle row, probably AN 1/2, pull up the fader). Then route the mic input to AES (pull up the fader on the top row), and check your pan setting. The signal sent to AES out is now available to software on the AES input. Note that TotalMix will not show the input signal.

You'll also want to listen while you're doing this, so let's set up a system to cue the AES out audio to Phones. In the bottom right of TMFX, Control Room, click the Assign button. Choose Main and select Phones 9/10 as main. Now click the green Cue button on the AES output channels, and you will get the same signal at your Phones out. You can even change the volume of the Phones without disturbing the audio recording now. Nice, huh?