If Moku:Lab only has two output channels, how is it possible to generate feedback control signals as well as the modulation tone and scanning waveform?

The low-bandwidth control signal on output channel 2 can be separated electronically from the high-frequency modulation tone using an external bias-tee (not included with Moku:Lab). An appropriate bias-tee can be purchased from Mini-Circuits.

The scanning waveform is typically applied to the same actuator as the high-bandwidth control signal, so no bias-tee is required to separate the two signals.