Yes, you can! This functionality is available in both SoundCheck 15 (native feature) and SoundCheck 14 (download links below).
In SoundCheck 15, Listen introduced a new custom step named Mixer Volume. When inserted into a SoundCheck sequence, this step can communicate directly with the Windows Mixer and can be used to adjust the Input/Output level of any WDM audio device.
The step can be found in the Custom Template folder and is inserted into a SoundCheck sequence like any other step. It offers the following controls:
1. Selection of device type (playback or recording)
2. Available device dropdown list
3. Volume level slider
4. Mute function
Figure 1 - Mixer Volume User Interface
The Mixer Volume Custom Step is also compatible with SoundCheck 14, meaning users of this version can download and install the feature into their SC14 folder using the links below. Complete instructions for installation and use are included. Take care to download the proper version (64 bit or 32 bit) for your version of SoundCheck.