It is possible to use a subwoofer alongside your MXW70 and DacMagic 200M setup.
To do this we would recommend using a balanced (XLR) connection between the DacMagic 200M and the MXW70, ensuring that the MXW70 input switch is set to balanced.
Connecting the units in this way leaves the unbalanced (RCA) output of the DacMagic 200M free to allow an additional connection to be made. As both the balanced and unbalanced connections run simultaneously on the DAC, you can use this output to connect a subwoofer within your setup.