I am not familiar with those sub woofers in particular, however, I have always read (from multiple sources) that if you are going to setup two (or more) subs, it is a good idea that they be relatively equally matched in terms of frequency response and dynamic range. As such, if one of those subs is significantly better than the other, then I would not recommend setting them up in the same room. Rather, I would use the lesser of the two in a bedroom, or office, or sell/give it to a friend. If you don't have a set-up in any of the mentioned rooms, then maybe it will be a good excuse to buy an additional receiver, and put your old speakers in the bedroom, or office, or study... or somewhere you might like to listen to music other than your main listening room.
**Edit** A second system, of lesser quality, in the garage is something I have always wanted, for working on the car/lawn mower/various projects. On second though, I imagine once I replace all of my current gear, I will be putting it in the garage, once I have a garage :-( This is more incentive for me to buy a house, and then upgrade...