Which Component Has the Greatest Affect on Low-Level Listening

Speakers.

a very well executed line preamp with attention paid to stable linear gain attenuation will have the most dramatic impact of fullness at ALL playback levels.
 






This is the best advice, it makes sense. I have 80 db sensitivity speakers and they sound great a low levels, plenty of good bass. My preamp made the most difference for low level listening, attenuation is very linear in my preamp.

I didn't count, but a guess the responses are 50/50.

I have been reading more since posting the question:

- horns (which I've never owned) seem to have good impact at low levels
- loudness (which I do have) also has made a difference

Maybe combining the two will produce good results:
Luxman's new integrateds
Klipsch Heresys or Cornwalls

Just thinking about some possibilities, since low level listening is about 90% of my listening from morning til evening.

Thanks for all the replies!

Higher efficiency speakers will allow your amp to go further and should help when bass is boosted by a loudness control as well. 
In theory.....proof is in the pudding. 🙏

No matter what amplifier I was using my Harbeth SHL5's and 40's always sounded great at low levels. All the Harbeth's I have ever heard have played very well at low volumes. Almost every review of any Harbeth speaker seems to mention this. From my point of view the speaker is more important than the electronics for a satisfying low volume listening experience. Good Luck!