Go with the 20-39pci.  In a large room, you'll want the extra output.  This sub still gets down to 16Hz with very usable output at the seated position.  Most people going with the 16-46 seem to end up getting a second 16-46 for added output.  Few movies utilize the 10-15Hz response the 16-46 is cabaple of, and at the added expense of output, the 20-39 IMO is the better choice.