Check that the pre doesn't have a +6dB switch somewhere - quite a few of them do.
Re: other issues - you might just have to accept that in your system, active pre's are better than passive. The D1 Driver may help, but at the expense of system complexity etc.
I've spent plenty of time with passives and there is a lot to admire in what they can achieve, but in my system at least, adding the right pre brought a certain magic that I couldn't find with a passive, even when a D1 Driver was added.
Without disagreeing an active pre-amp may be a better match for whatever reason, for example with the Heisenberg power amps the matching Stern pre-amplifier is simply a "must have", the Bespoke does behave different to "standard TVCs".
See here for example:
https://audio-creative.nl/recensie-2/the-bespoke-audio-company-tvc-preamplifier/
The frequency response measures identical into a 10, 50 or 100K load, even a 300 Ohm load which you wouldn't find in any power amplifier afaik is ok though at -1dB (light green line in the first graph on that page. -3dB at 100KHz and a well damped 160KHz resonance. THD+N is below -130dB, the 50Hz peak is due to transformer hum from surrounding equipment, so it;s practically at -140dB.
The Allegri reference is an autoformer, not a TVC, all FWIW..