My gut reaction is that apartments and subs don't mix well. Of course, it all depends on how well sound isolation has been implemented in your building and the volume at which you typically listen.
Plus, although you have a good receiver, running those four towers full-range may be demanding on its power supply. Again, depends on the volume.
With no other info to go by, I vote for adding the amp. Good luck with your decision.
Too bad about the medical bills - hope all is well. If you lived here, you wouldn't have had to sell your emo's! Then again, if you lived here, your emo's would've cost you a
lot more....