What version of FCP X are you on? There is no 10.7.5, I'll assume you mean 10.0.7, the latest version.
I have no clue what "TBT" is.
To start with record your audio directly inside of FCP X.
Window menu, "Record Audio".
FCP X will recognize your AJA devices. I use them in my own studio.
Edit it up inside of FCP X. Here are three links with info about doing this. These apply to anything you're recording, not only voice work.
When you export, you need to set up a custom "Destination".
File > Share > Add Destination.
Double click the "Export File" icon in the right hand section of that window.
In the left hand side, where it was added, rename it "MP3 Export".
With it highlighted, in the right-side pane, set it as thus:
Format: Audio Only
Audio File Format: MP3 File
You can set chapter markers as you wish.
Set "Open With" to "Do Nothing".
Use this for your exports.