Hi Rick,
Here is the step by step process for doing what you are asking (My assumptions are that you are familiar with the QU desk. I am using the QU-32, but you can apply the following to a QU-16 also):
1. Select the Setup tab on the right of your touch screen.
2. Go to the I/O Patch and select the USB tab
3. On 2 unused channels (for me – Channel 31 and 32) touch the first channel and then using the rotary dial on the right of the screen, cycle through the options until you hit MTX 1 L. My Channel 31 says MTX 1 L. Do the same with the next channel – My channel 32 says MTX 2 R. This way you are selecting to send your Matrix 1-2 as stereo outs Left and Right.
4. Select the Main LR out with the green Sel button and then select the Routing tab on the right of the screen.
5. Select the Matrix Sends button and then touch the Post button to make it a Pre out. This routes the signal from the Main LR to the Matrix as a Pre Main fader level signal, while not touching your Main LR volume out.
6. Using the rotating dial on the right, touch the level button at the bottom of the screen, and then you can add a DB boost to the signal being sent to Channels 31-32 for me (whatever you assign them to).
Then in Logic, you can select channels 31-32 as your recording channels and you should have a DB boost for your recording.
Hope that helps.
Clayton