Do all Passive preamps exhibit this trait

Lack of dynamics hasn't been my experience with any of the passives I've owned:

Promitheus TVC
Sonic Euphoria (autoformers)
Bent TVC (S&B trannies)

In all of these cases, dynamics seemed explosive, not lethargic. The presentation also seemed airier and more detailed than actives in the same price range. I've heard the new Bent passive with Dave Slagle's autoformers and would say the same thing.

I don't doubt the calculations show:

passive controls traditionally limit dynamic contrasts and bass impact as you turn the volume down, due to the interaction between the cable, the input of the amp, and the control itself

but in practice, these shortcomings were minimal or inaudible in my system. This was especially true of the Sonic Euphoria and Bent with autoformers. Low level listening with these passives was a pleasure. They had a fullness at low volumes that seemed more natural and proportional than an active.

However, a back-to-back comparison of the Bent TVC and an Audible Mod3a indicated something was missing in the midbass area. A friend and I both agreed that the Mod3a was noticeably warmer in a good way. After a year of intense interest in passives, I've returned to an active, but I still believe a good autoformer-based passive will outperform most actives in the sub 1000 category.

Lornoah, I can't comment on the GFP-750, b/c I haven't heard it, but I'm fairly certain it doesn't use transformers or autoformers in passive mode. Potentiometers are the most common attenuator and it wouldn't surprise me if this is what the 750 uses. If this is the case, it would explain why you're hearing these shortcomings. A potentiometer can't preserve the impedance curve of the source when the volume is turned down. Ralph (Atmasphere) explains the technical details up above. But I do know that transformers and autoformers do a much better job at preserving the impedance, and this is why they sound better. You should be able to hear this difference in a resolving system. I certainly did when I compared a Creek OBH-10 (potentiometer-based) to a Bent TVC. The Creek was no match. The Bent had a more open sound and better frequency extension in both directions, but especially in the bass.

Does anyone know of a passive preamp that will provide me with this treble extension and at the same time sounds relaxed with no listener fatigue. Thanks.
Lornoah (Threads)

All of the passives I've owned had excellent frequency extension and no fatigue. There was no premature decay in the upper registers. They presented music with an abundance of air and detail.

If you want to stay with a passive, I recommend a Sonic Euphoria or a Promitheus TVC. They're both common in the classifieds and their tech design is more mature than the 750.

I forgot to mention Dave Slagle's latest DIY passive that Clio09 pointed out. It's based on the same autoformer that John Chapman uses in his current Bent line-up. I absolutely doubt you can do better for $350.