Low Volumes

As Larryi suggests, the bass energy is easily transmissible in many cases. In mine, it is not the bass energy which comes through (unless one is right beneath, but my speakers are placed where it is impossible for my neighbors to be under) but piano. YMMV depending on the materials/construction between you and your neighbors Many horns will be deficient in deep bass, but high efficiency bass drivers can do low SPL bass quite well I find, and as long as the bass drivers are high efficiency, integration can be handled well enough.

You might consider bringing your speakers further out into the room. This should help reduce the bass reflections off the walls and help keep them from resonating, like a subwoofer in a car turns the whole car into a big resonating object.

Good luck.

Jim

How about a pair Magnepan 1.7 speakers with an Audio Research 100 watt tube amp. I think it would sound great. It would not go loud but that is what you want.

As an apt. dweller and the manager; here's how it goes: Your neighbor shouldn't even be able to know your stereo is on-- after 10pm. Meaning; if they can hear it,it's to loud.This applies to TVs, more often or low priced stereo systems. (There are no audiophiles here.)
I got 94 units and there are many types here. Some can hear a mouse fart,three floors above;(and they will let you know about it.)
I do have a unique advantage. When the apt. next to me is empty I can go over there at 3am and listen.
I have 4x8 panels of "sound board",from Home Depot; lining that wall.--That sucked the life out of the music so I had to add vinyl covered panel over the sound board. Also, this does nothing to control the bass,period.
My solutions are a great power conditioner;great cables and great components.---As to extract all the music---or as much of it as to be satisfying at lower listening levels.

Like Avguygeorge, I have some experience with managing rentals (8 years as a resident manager). While I agree that the presumption favors the complainer, and if it's audible at all in other units, you may get shut down, many jurisdictions have language like "peaceful enjoyment" which is probably not usually interpreted as a "right to silence," esp. before 10 or so. (Think of ordinary conversation, the sound of footsteps, or a baby crying.) In practice, and maybe in theory, I think managers (and judges) operate with a "reasonable person" standard, so that it helps your case if you can show that the music is not blaring. Elizabeth's suggestion of appealing to measurements could help you make your case, if you're unfortunate enough to live near someone who is always listening for mouse farts. John