Deep frequencies are deep frequencies. Porting won't matter, subdudes and grammas will absorb some mechanical energy but not the noise. If you have neighbors and you buy a serious subwoofer, you will bother them if you playback anything at any kind of loudness you would enjoy. The only way around this is if your buildings construction is thick and solid, and there is a firewall between you and your neighbor. The situation sucks for you, I am sorry to say, but don't kid yourself, you can't be a good apartment/condo/townhouse neighbor and rock out with a good subwoofer.
Perhaps if you know your neighbors, you can talk to them and reach an understanding, like its cool with them if you rock out during the afternoon, but not late at night. If it were me though, I would just get full range tower speakers and forget the sub for the time being.