Which preamp helps lower listening sessions?

i can think of a few diferent ways a system can sound better at low levels.

in your case, going from the Simaudio ss to the tube preamp, the tubes likely have a warmer, more full character which can satisfy at lower levels, whereas the ss preamp needs to 'get going' before the body and fullness of the music come thru. ss can sound lean and light weight at low levels.

another thing can be the room or speakers or a combination of both. at lower levels room issues are minimized, both in the low frequencies and the highs. depending on what issues there might be low listening levels might avoid those issues.

in a perfect world a system and room is optimal at many different SPL's; since each recording has an ideal volume, and as our moods change so (sometimes) does the volume. if you only listen at low levels your musical choices will get much narrower.

I often listen at low levels also. I like the upper model Conrad Johnson tube preamps like the CT-5 and ACT2 series 2. These use the 6h30 tube which has more extension at both ends than a 6922 (a favotite of mine) which will help at low levels. They are the only preamp I have heard of that uses just one gain stage and has no cathode follower. That cleans things up even more. All this means nothing if it's not implemented right but CJ has a pretty good reputation for their preamps.

I don't think you will find a preamp that "compensates" at low volumes. I suppose it could be done. The Bose Radio has a circuit inside that adjusts freq response at low levels but just because it doesn't have tone controls doesn't mean it's a "straight wire". How about turning up the subwoofer at the low levels to compensate?

TRL Dude. One of the traits of TRL designs is that lower listening levels produce excellent resolution without frequency loss. Another trait is the designs yield highly musical results. Nothing artificial or exaggerated.