I narrowed my search to these 3 line stage preamps, 2 released 2019, 1 released 2018. Please comment if you know or suspect one may outperform the other two.
For this discussion disregard price differences; imagine all 3 have similar SRP, which they don't. (FYI Tortuga w/1st cap upgrade $3450, Linear Tube Audio/LTA MZ3 $3700/no upgrades offered IIRC, Kinki Studio w/shipping and tariff about $2300/no upgrades offered except a Goldmund type face plate.)
IMO these 3 line stage preamps offer the best value and best performance for my needs listed herein. Better performance likely costs at least 3x more.
Please suggest other preamp only if it fits my needs listed herein, it has SRP under about $6k, you AB tested it vs. one of the subjects (or a derivative listed herein), and you preferred that other preamp (that's a lot of qualifications).
Important: the associated speakers have wide range tuning functions including active distributed sub array and gain and tilt controls for mid-treble crossed @ either 750 Hz or 1.3k Hz (depending on the model). The speaker tuning functions eliminate or almost eliminate spectral differences between the preamps.
Derivative models w/same performance: LDR3000T released mid-late 2019 is one box combining the earlier celebrated passive 4th Generation volume control + outboard tube buffer w/3 gain settings (0, +3, +6 dB). Of the 2 cap upgrades Tortuga offers I would get the 1st cap upgrade, about $440. The preamp stages are identical in LTA's $3700 MZ3 and $4400 "Preamplifier" model (both released 2019); both models are LTA's all time best preamp stage by yuge margin.
My line level preamp needs:
1. Remote volume
2. Unbalanced OK
3. Switch between 3 sources, tape outputs irrelevant
4. Requires current capacity to drive load impedance as low as about 8k ohm, comprising 12k ohm sub amps and a wide array of different main amps.
I suspect and shall confirm all 3 subjects meet all needs. That's it. Any other feature is unnecessary. Internal DAC is fail, period, full stop. Headphone feature is irrelevant.
This is likely my last active line preamp purchase; I want it to last for decades. If the preamp has an LED I plan to buy a spare LED for future replacement. IOW long term service is yuge.
Tortuga: US made, nice. I lean this direction. Srajan/6moons slightly preferred the $15k Nagra Classic tube preamp over the Kinki; I hope the Tortuga performs more like the Nagra. Dave Slagle is one of my heroes; he used to make autoformer volume controls. I hope Tortuga's LDR volume control performance equals or beats Dave's autoformer volume. Switchable gain of 0, +3 or +6 dB via a triode tube followed by a SS current buffer. Did not check the PS type.
Linear Tube Audio microZOTL MZ3: US made. Employs Berning's "Zero hysteresis OTL" circuit alleged to improve tube performance by modulating the music signal atop a carrier frequency (150k or 250k, forgot). Advertised to increase tube life, but it employs 4 tubes to Tortuga's 1 or 2 (forgot). Highly refined ladder-resistor volume control. Deluxe linear PS.
Which weighs more on performance: Tortuga's volume control, ZOTL's unique gain stage, or is it a wash?
If it's a wash I may lean toward LTA for it's more common parts and technology improving odds for long term service and parts supply.
Kinki Studio: all SS/no tube maintenance. Chinese newcomer but reviewers rave about performance. Gold plated PCB traces. Separate transformer per channel each isolated in alloy sub-enclosure. Internal images evoke a $10-15k preamp. Long distance service from China (manufactured) and/or Singapore (international sales rep). Kinki replied quickly to my email. Per Srajan/6moons: the only thing clearly better, and only marginally is Nagra's $15k Classic tube preamp.