Most impactful for playing soft

Integrate a nice subwoofer to fill out the lower registers. 

I’d look at properly applying DSP functionality in products like Roon or miniDSP to help adjust for room acoustics. Adjusting for room acoustics addresses the root cause and allows all the music to come through cleaner and better at all volumes. 

     Here's why, at lower SPLs, your system's lower freqs sound weak:

https://www.teachmeaudio.com/recording/sound-reproduction/fletcher-munson-curves

     Most older receivers had a 'LOUDNESS' function that boosted lows and highs to compensate for the typical ear's curve at lower volume levels.

              http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/eqloud.html

Listening in Ultralinear is NO CO$T and should be used.how about headphones? The PL has a good headphone section. 

Longtime PL user here. KT 150's will give a more impactful sound, which might be noticed during low level listening.

As mentioned-room/speaker setup and  DSP to confirm what's going  on, if you want absolutes.

I had a friend over last night and we listened for hours. Couldn’t believe how great the system was sounding. House was dead quiet and the room was full. I pulled out my phone and the sound meter said average in low 50 dB. I didn’t believe it so I pulled up another ap and got the same thing.

The downside listening at low levels is it is hard to talk under the music. You end up not talking to listen. Or waiting for a less favored song.

Of couse I listen by myself most of the time.

To me, and many will disagree, the first step in excellent listening at low levels is to choose the right system strategy. Many choose low sensitivity speakers and high power amps. I’ve found my preference (a very strong preference) to be sensitive speakers and SET tube amps. I’ve tried many SETs and none were bad but many had weaknesses. Right now I’m using a little 2.3 wpc amp from Decware. I have a custom 4wpc amp under construction. I’d recommend starting with Decware if you can find one or Aric.

The last thing I did to really add more boom to low volume listening is to buy a DHT based tube DAC that also works as a preamp. DHTs are pretty much top of the heap for me. My new amp will be DHT based so I’ll be feeding DHTs with DHTs. This is pretty expensive. Before this I had Chord DAVE which I was very happy with. A friend who is as knowledgeable about high end audio as anyone is still litening to a Chord Qutest--a huge bargain in high end digital.

Feed that with a quality streamer, and many people have their favorite brand, I just went from Innuos to Grimm, but they all are great in the $5k price range and up. In a lower price range I’d go with some of the Innuos offerings.

As for speakers, I've never found horns that sounded great to me.  I'm listening to a 4 way speaker with 96dB.  Full range, floorstanding, great response from top to bottom.  Tekton if a huge bargain, focusing on sound rather than cabinetry but won't go well if your in a room with $100k in fine furniture and decorattion.

Best of luck,

Jerry