Most impactful for playing soft

Speaking plainly, I consider what you have just observed to be the difference between your system and the next level up (maybe 2 levels if you take small steps).  

To get to where you want to be I'd replace every component you have named.  

Jerry

During my journey I've found the better the system the less need to want to play it loud. (85-95 db) and the quieter the music seems because the 'space' is more accurately presented. 

After getting my system components in place I noticed power cables made a difference in the clarity and presentation of low frequencies.  It was very unexpected to me.

Not so fast…human hearing requires a loudness curve for a reason…

How loud ( spl ) is the spouse acceptable level ?

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

I have also observed the better the system, the better it sounds at low volume. Each tier up sounded better at lower volumes. I suspect that there is more to it than that. That a sub $100K system can sound great at really low volume. But I am unsure as to what it would be. But once my system broke $100K it started sounding spectacular at low volume.

Yes, best of luck. This sounds like a decade or longer search to find the key.

A receiver with a loudness control :)

@secretguy -  

         A receiver with a loudness control :)

                                 OR: DSP

      (with which to program a little boost, at times*)

  But: let's not deprive the fact resistant of their beloved chasing-of-the-tail (with *the answer).

https://www.extron.com/article/loudnesscontrol_ts#:~:text=The%20loudness%20control%20is%20simply,treble%20appear%20to%20be%20lacking.

@milog -

     One can preprogram a number of freq response ("loudness") curves, with one of these devices, for those special times:

       https://www.minidsp.com/applications/dsp-basics/system-equalization

I’m using a little 2.3 wpc amp from Decware. I have a custom 4wpc amp under construction.

@carlsbad2

Sounds interesting. Any thoughts on GLOW Amp One Single Ended Tube Amplifier - SPECIAL EDITION

Without a Doubt it is the difference of humans hearing various frequencies at low volume, as documented by Fletcher Munson.

The biggest difference a LOUDNESS (stupid name for a low volume listening adjustment) is boosting the BASS. That is what maintains involvement, keeps low volume from becoming background music.

Tone control, boost bass some should perk things up.

Lots of modern equipment omit tone controls, most omit 'loudness' eq circuits.

The Chase RLC-1 Remote Line Controller unit I mention tooooo often, has an automatic and progressive Fletcher Munson curve that begins at low volume, and increases progressively as you further lower the volume.

you can download manual from hifiengine

https://www.hifiengine.com/manual_library/chase-technologies/rlc-1.shtml

this one is ridiculously overpriced, but it shows the unit well. They pop up occasionally for around $100.

You need the remote, no controls are on the unit.