TVC Gain effects

A lot of TVCs, like my AudioZone, can produce gain, usually 6dB. The AZ does this with a switch (I think the Bent just engages gain automatically once you're above unity.)

Does anyone know what the effects, if any, on output Z and frequencey response are of engaging gain?

I tend to prefer the unit with the +6dB setting engaged, even at lower volumes.
The additional 6 dB of gain affects impedance issues for the worse. For the S&B, the input impedance would be 2500 and the output impedance increases. Obviously, that isn't a problem or you prefer the frequency extremes slightly rolled off.
Thanks! I did find this information on the S&B page as well.

I guess it is better to use a volume setting closer to unity gain (-8 or -12dB usually) with the 6dB switch off then to keep it on with a lower setting.

With a source Zout of around 30 and amp Zin of 100K, you might say I have "impedance differential" to spare, but still..

Some say that they prefer the trannies with the extra gain, which is probably a little strange.
The Audiozone Pre-T1 TVC preamp tends to sound a bit better with the additional 6db of gain- don't ask me why...
Would that go for any S&B tranny implementation, then? Hard to see why it wouldn't.

Does anyone have any guesses as to what could cause such an improvement with gain? Other than that the induced response variations end up correcting for some other problem in the chain?!
Does anyone have any guesses as to what could cause such an improvement with gain
You have current to spare -- but are lacking in voltage. I.e. yr source outputs a lot of energy -- but lower voltage than you like, or than the amp likes -- the latter admittedly, being strange as most amps reach their spec'd limit @~1,5V. (Upping the voltage on the tranny, you halve the current -- all other things being equal.)
My source is 2V and amps' sens. 1.1V. I'd "thought" that the +6 setting sounded better to me, too, but then I learned that I was wrong on paper. :-}
There are 2 explanations I can think of:

1) The higher gain setting will likely result in some sort of rolloff, probably at both ends of the frequency band. This could provide a filter effect, i.e. a synergistic effect that might be pleasant in some systems, through the mechanism of reduced bandwidth. Often that points to ultrasonic noise or other out-of band information (like actual audio information) that the power amplifier lacks the speed or power to reproduce without distortion.

2) TVCs can ring and are more easily loaded if used in the gain setting. It might be to your advantage to find out where critical damping occurs with the device, although that is probably tricky as it changes with each setting of the control. Hopefully the designer recognized this problem and built the loading into the unit, if so then #1 is your answer.