Yes Sigma is compatible with Studio One 2 on both Mac OSX and Windows.
Set Sigma to use the Logic (MCU) profile.
In Studio One Preferences/Options add a Mackie Control set to use the first Sigma ipMIDI port (channel 1-8) as defined in the Sigma browser > press OK.
Now add a Mackie Control Extender in Studio One set to use the second ipMIDI port (channels 9-16).
Press the 'Placement...' button and drag the Mackie Control and Mackie Control Extender into the same control group, ensuring that the Mackie Control is on the left.
Press close and OK to exit the control surface windows.
Studio One offers 10dB of fader gain above unity. Above 5dB the correlation between the Sigma level and the Studio One fader becomes non-linear. It is therefore recommended to avoid using the 5dB > 10dB range of the Studio One fader.
Note that ipMIDI should be configured with Loopback = OFF.
On Windows this can be configured by navigating to Start Menu>All Programs>ipMIDI>ipMIDI Monitor.
On Mac OSX, navigate to Applications>Utilities>AudioMIDI Setup, then Window>Show MIDI Window. Double click the ipMIDI icon to edit the Loopback state.