What will a preamp do for me?

To the OP, I will chime in....." Loud rock sounds flatter, less dynamic than I’d like ". Loud rock is not Thiel territory, and, with a tube amp ? Not to sound crude, but you have it all wrong. I am also a convert to passive, as I no longer want to "color " my recordings or hear less " detail and information " from my recordings with an extra gain stage or 2 that I do not need. I am the happy owner of a Luminous Audio Axiom II Walker mod unit, and have never been more pleased with what I am hearing from my recordings. Elizabeth.....3 separate gain stages ( Threshold to CJ to Bryston ). Really ? Enjoy ! MrD.

elizabeth, are you running your source signal through three different linestage preamps daisy chained and at the same time or I’m reading it wrong? Highly unusual setup.

Yes, I'm curious too, 3 preamps in series???

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.

Short answer, yes I am daisy chaining three preamps at this very moment.Debussy in the five disc changer I paid $40 for on eBay$125 Toslink (Lifatech) from that to my $7,000 fancy DAC (or SACD player, your choice but you ask why not just use the spinner in the $7K wonder??? ahhh lazy, five beats one for lazy) The Balanced out goes direct to Bryston BP-26 when I want that. the single ended to the recently bought Threshold FET10 linestage, and from there it can either go to the BP-26, or to my Conrad Johnson ACT2 which in turn feeds another input to the BP-26.                                          
So at the flip of the selector on the Bryston I can hear direct via XLR (Cable is Cardas Parsec) from Marantz SA-10, single ended )able is Kimber KS1016) SA-10 from the Threshold, or single ended SA-10 from the Conrad Johnson via the Threshold(with a Cardas Parsec TO the Conrad Johnson, and a Kimber KS1016 to the BP-26). Direct XLR is the tightest, clearest, alas slightly boring. From the Threshold, more body, more bass and alas, slightly ’dry’(but actually real good). From the Conrad Johnson, ahah! That old second hamonic kicks in... Just right. (everything else stays on 24/7. Sadly the Conrad Johnson ACT2 is blast furnace hot for a preamp gizmo, and only on when used, and yes that is it’s normal state. Curiously the Threshold is stone cold when left on/in use, so is it’s power supply)The difference between choices one two and three is very very tiny. But hey my ears, my money, my choice.
And I LIKE preamps... I own several more... An Audio Research Sp-15 an Audio Illusions Modulus 3A, and a Onkyo Grand Integra P308. Plus the not working VAC Standard in the closet.