You were very polite there Mr Wolf that you didn't go for the other descriptor you had mentioned in your post..
Just playing!
But Tuppence, on a serious note, a subwoofer in an apartment is definitely reasonable. You just have to tune it to take over the low end without causing earthquakes. Its really not that hard given most of us buy £1000s worth of subwoofers to try and produce those earthquakes but still can't quite manage it. I'd have sold you my BK mono + for a song but I've decided to keep it now but I'm sure a comparable/better/cheaper deal is available on classifields.
I'd be happy to try and find you a deal or help out in anyway I can. Subs are excellent additions to an experience trust me, just finding the right one and tuning it properly. Or better yet, I can REALLY help you if u want to go down the hoverboss route. Its probably the best resolution to get as close to full fidelity low end impact without the neighbours realising as its literaly woofers firing into you.. but the cost and time effort is a bit high.