Go to channel setup of the channel which has the analog out option. Click the "AO..." button and change the output to output math. With the checkboxes, you can choose the analog in channels which will be output. If more then one channel is used, Sirius will SUM the channels together.
After everything is set up, go to channel setup, right click on the top of the "Ampl. name" and choose the "Set power on default option".
Unplug the Sirius slice from USB and power supply. When the Sirius is connected back to power supply, it will start outputting the signal out of the analog output.
The sampling rate with which the Sirius will work is the same as the channel setup sample rate. This can be set in Dewesoft settings: