What will a preamp do for me?

But, according to Paul, todays controls are extremely linear. He also explained how even the best non-linear controls increase noise levels at lower volumes, and can not compete with today's digital controls.

I can safely challenge the idea that analog controls are noisier than digital at low volume levels. The statement is false. So much depends on execution- a general statement like that just can't hold water.
Preamps serve 4 functions:
1) control volume2) select the source3) provide any needed gain4) control the interconnect cable to the amplifier
The OP does not need 2 and 3, but 1 is essential and 4 is the least understood. The problem is complicated by the fact that a balanced system is mandatory. FWIW there are no passive volume controls that support the balanced standard, which is there to prevent the interconnect cable from having an artifact (the 'sound' of the cable).
For that matter there are not that many active line stages that support the standard (also known as AES48, the Audio Engineering Society file 48). But there are a few, and if a balanced system is thus set up correctly, then the interconnect cable will not influence the sound.

Well, I am not going to chain together three pre-amps, at least not any time soon, but I do appreciate all the ideas! 

elizabeth - I read with interest your thread titled "how do you know which component to upgrade" and found it very insightful, except for the fact that it ultimately didn't answer my question, not that I really expected it to :).  But I am happily following your advice so far, as left for me on a similar post, kind of a false start to this one.

atmasphere - I am dedicated to keeping all things balanced.

mrdecibel - 85% of my listening, and nearly all of my critical listening, is a mix of Americana (Tidal's nomenclature, aka folk, alt-country, chamber pop, laurel canyon pop, jazz pop, non pop radio pop, alt/indy, some but not all rock-n-roll, etc) as well as jazz and classical, generally at 75-85 dBs.  To my inexperienced ears, my system sounds pretty darn good for this type of music in my room.  It just bugs me that when I want to rock out, the sound is not as enjoyable.  Ditto the treble.  

gosta - I love the Theils - for now.  Speaker upgrade is well out over the horizon, but certainly out there, albeit way out in the future (2020 maybe?).  My goal for now is to make the 2.3s sound as good as possible, maybe even upgrade the crossovers, before moving on.

all - sounds like there possibilities both ways, my conclusion so far is that ultimately what I am looking for COULD be achieved without a preamp, AND it's also likely that the RIGHT pre would also make me very happy. If the right pre is right to me because it colors the sound a certain way, perhaps I can get there following another path?

So far I have improved isolation of the amp (moderate improvement) and plugged it right into the wall outlet (also a moderate improvement).  Next up is a Furutech wall outlet (Rhodium plating, "Rhodium especially excels in the high frequencies which are detailed and clear. Overall rhodium yields a super responsive, delicate, expressive and neutral sound…" - we'll see.  Then I think I will try some NOS 6SN7s, old Russian tubes from Upscale, in place of the current Sylvania Chrome Domes.  Upgrading the source to a PS Audio DSD is the next big component improvement.  After that, speaker isolation? And then, maybe, the Schitt Freya, because it is balanced, gives me three modes of operation to play with including passive, (four if you count the Octal LISST option) but even more importantly, it can be returned (it will be a tough 15 days of burn-in and listening, but if I plan ahead, I think I am up to the task).  And of course, room treatment will continue.  Or maybe I will come across what could be the perfect pre-amp at a price that not buying would be very regretful, who knows, it could happen! 

More advice is welcome!  

Just discovered.
Elac Alchemy DDP-1. From their new digital serie. May be of interest.
Combine with streamer DMP-1. Has AES output which could be led
directly to pro monitors with digital input. Becoming rather common.

Basically a preamp will make whatever a DAC does, but better. A preamp is a must have item in any hi end system. I was not enjoying my system and messing around so many things trying not to expend money on a preamp. I was partially convinced to buy a preamp. I did then bought a used hi end one. That was amazing. That was the best improvement I did I my system. Sounds were then clearer, better played. I think it is a good improvement you can do for your system. Today, if I had to start a new system, that would be my first bought. That is the brain of your system. The amp is the heart and the speakers are the legs.