No. SPDIF is a fixed voltage level output, level control in UC is not possible. You have two options:
Control the volume output from your DAW, ie the level you send to your SPDIF output in your DAW, consider making an AUX Send and controlling it with an output fader (the level you send to SPDIF.
Connect the SPDIF output to a Monitor Speaker controller with SPDIF Input and use the knob on the monitor controller to control levels to your monitors. Ie Monitor Station II or Central Station.