So I tried my SB16 Ultra from upstairs and I like it so far, I understand what you all are saying about more output coming from the PB4000 but to me in my room the SB16 sounds just as good/just as low! For me it was hard to distinguish the differences between the single PB4000 and the SB16 (of course just by ear) comparing the same movie scenes between the two.
So I think I will return the PB4000 and buy the second SB16 to run duals. (locate them on outer sides of Ultra Towers)
In my 14x20 media area, the SB16 packs a nice punch and I can only imagine what a second one will do to add more impact and level out the bass throughout the entire room
The room I took the SB16 from is a closed smaller area, I had an older svs ps12 so I stuck that one there which works good for now (probably upgrade to SB3000 later)