Learned that the hard way. Bought a VTF2MK4, which was nice, but did not have the ooomph for my room. Later sold it and got a VTF15 (Considered Rythmik and PB13). Later added a second VTF15, and that made the difference in freq response. After that I upgraded from small def tech speakers to the...
Two subs are generally better than one, the issue for me is, is dual bics going to best the VTF2. That Im not sure of because I have never owned a bic. I do know when I had the VTF2 MK4 in this room (over 5300 cu ft) it performed very very well.
Just looking at your PB1000 budget, look here too, not a fan of 10" for movies:
http://www.rythmikaudio.com/LV12R.html
http://www.rythmikaudio.com/L12.html
http://www.hsuresearch.com/products/vtf-2mk5.html
And yes, Id go ported.