Speakers for low-level listening

I would suggest adjusting your five band equalizer to see if you can get the sound you want at low level with your current speakers before purchasing anything new.  I have an MA8900 and due to my neighbors (I live in a townhome) my late night listening is often somewhere between upper 40s to mid 50s db.  It’s around midnight right now and I’m around 50db but I have tweaked the equalizer to accentuate the higher frequencies.  I’ve got a couple of subs so I actually have to turn those down a bit even at low levels.  I find it very enjoyable to listen late night.  I still get a very good soundstage and imaging and it’s so quiet everywhere else it feels louder than it is.

I have a McIntosh MA 8900 as well.  Mine is paired with the Klipsch Cornwall IVs.  I listen at low levels most nights, I haven't felt the need to mess the the EQ at all, I seem to be able to get good frequency extension without it.  

I have to second or third the headphone idea. I have a separate headphone system myself and in many respects rivals my main system… while different it is inspiring and compelling each time I listen to it. I will say it was as much effort assembling as my main system. My systems are shown under my userID.

To expound on my advice to try headphones..
 With your amp,the Sennheiser HD800S would be my budget choice,boasting some of the most amazing imaging & sound staging available from headphones at any price! They also offer a beautifully voiced mid range & treble but are a little bass lite compared to more expensive choices...Moving higher up the cost chain I only have direct experience with the HiFiMan Susvara,which is quite simply for myself,the stuff dreams are made of...
 

Schiit Loki Max equalizer. Game changer for my system. Especially helpful to tailor my speakers to my desired listening level, including low levels.