While you are waiting to hear from Gary I think it is safe to say that the second pair of outputs on almost any preamp are in parallel (duplicate) the other pair and can be used to drive a powered subwoofer. The full range signal goes to the sub which strips off the highs (low pass filters) and reproduces just the low bass. And, of course, your preamp controls the master volume for both. This is at least the way it has worked with all the preamps I've ever owned with extra outputs, including my Dodd Audio Battery Pre. The exception would be a "Home Theater" output found on some preamps. This is also a full range output but taps out before the volume control so your HT system can use the stuff connected to your audiophile preamp but the volume will be handled by your HT controller. Of course, this kind of output will not be suitable for driving your sub since you lose control of volume. However, these outputs are usually clearly labeled "Home Theater Bypass" or somesuch or are selectable by a jumper or switch on the preamp.
