Best Late Night Low Volume Speaker

Mentioning brand names will not make sense, as it will be the synergy that would please "your" ears.
I would look into many highly regarded components, known for the above. Need to make sure you have good AC as well. Cables, isolation stands make sense.
For the speakers it depends if you want near field, for which a highly regarded monitor should work. But if you are picky, then a very large speaker with a lot of "surface" area can probably deliver the presense without getting too loud.

Or you can say hell with it and go with headphones, and a good amp. There is a new component out there which will stimulate your speakers/room for you though the headphones, so you can listen at normal volumes, and still get the feel of real stereo.

Triangle Titus XS or Comete won't break the bank and are exceptional low volume speakers if not quite the "best".

Hawthorne Audio OB's driven by a simple 10 watt SET 300b integrated. Hands down, the most crystal clear presentation...I know because I'm having to listen late at night while the my other half is sleeping.

A good pair of headphones (such as the Beyerdynamic T1 or Senn HD800) and a dedicated headphone amp.

Wilson Watt *8