Just some preliminary pictures... I'll post the writeup later.
This is a Valley People Trans-Amp Mic Pre. No, this is not a discrete opamp like the 990 or API2520. This is a complete mic preamp in a "box."
The Trans-Samp have 9 pins at the bottom. I used some Mill-Max pins to socket them to the breadboard.
Here's some photos of output waveforms. Here, you can see the opposite polarities (or phase) from the (+) and (-) differential outputs.
Upon closer inspection, I see that there are some oscillations on the waveform.
Selecting the right value for the ceramic capacitor fixed that oscillation.