I live in a Victorian terraced house. My neighbours on one side are partial to getting pissed and playing godawful music way too loud at 2am. SO far, reason, polite requests, banging on the wall and shouting have had no effect. We have decided that producing a child will probbaly be the best way to get our own back....
OK, serious answer:
It will be *slightly* better for next door if you move the speakers to the opposite wall (mainly because of the dissipation of some of the bass).
Best, however, is to accept that, at certain times of the day, headphones are king.
Go to a hifi shop and listen to a decent pair. I mean something that costs a minimum of £100, preferably £250, and if you're serious, some Stax (the cheapest Stax come in at around £400 IIRC). Then, to go with your phones, buy a decent headphone amplifier.
You'll have sound so good, you'll wonder why you bother with loudspeakers at all.

