It depends a lot on the rest of your system. In home cinema it makes sense, at least if you're sticking to THX approved components throughout. If you've got very sensitive horns, like some who have posted to this thread, 29dB of gain will be WAY too much. Another argument would be that sensitivity should be standardised so that amps reach full output at 2V unbalanced or 4V balanced input, the de facto standard(ish) output for DACs. Pick an amp with more or less the power you need for your preferred maximum volume. But there will be counterarguments to that one too.
tl;dr: The power amp gain does not matter all that much, unless you use it to make the amp smaller and reduce output.
What is most important is to match gains for the typical volume position on the pre-amp. Let's pick a few pre-amps. I'm going to have to link Stereophile reviews for this since older ASR reviews often don't include SINAD vs output voltage chart for line outs, and it was just taking too long to find two good illustrative products. So, we'll go with this. First, Eversolo DMP-A8:
https://www.stereophile.com/images/0724-ES-A8fig03-600.jpg. Next, Topping Pre90:
https://www.stereophile.com/images/122Top90fig03.jpg. The Eversolo is effectively completely quiet from 1V to a whopping 15V. .0002% or -114dB in the whole range. The Pre90 doesn't appear to approach that until a huge 5V out, where it quiets to -108, or .004%. At 2V, it's .0025, or -92dB. Notably, this is
worse than the best AV receivers, which are ~110dB at this point. (Note: I don't know that something didn't go wrong with the Pre90 here, it's MUCH quieter in the ASR measurements, but that's not relevant for this example. I just needed some charts with appropriate curves.) Let's just call those SNR measurements, since they
mostly are since the curve is still sloping down.
If I need 100W and my amplifier is -95dB at 100W, and it reaches full output with 2V (which is maybe 25 or 26dB gain), I have hit full quiet (-95dB less a trifle) with the Eversolo and a typical AVR. But here's where it starts to get fun. With the -110dB AVR the overall noise is -9593. With the Eversolo? -94.95, maybe. I didn't get much extra. With the Topping? -90. Now let's say I have a "low gain mode" on the amp, and it requires a 10V input to max it out, and allows the amp to pull another 4dB to get to -99dB. Obviously, I can't use it in this mode with the AVR. It's probably out of the game. But I can with the Topping and the Eversolo. And it does get me something. With Eversolo, I now get -98.8dB. With Topping, I get -98.5. So, I've picked up something, at least, but not all that much. And I had to spend a bunch of extra money to get there,
and can no longer use my AVR preouts.
To stay on topic, the B100 will at least hypothetically always allow me to lower overall system SNR by blowing more voltage out of the preamp (as long as the preamp doesn't start distorting). The "problem" though is that it does nothing for me. Even in high gain, I already get -135dB noise at full power. What speaker can take advantage of that even at 6 feet from the speaker? Almost none. By 2V (on ASR measurements) Pre90 has hit -116. Total system noise is -115.95. I need 99dB horns just to take advantage of
that from only 6 feet away. At 9 feet, 104dB sensitive horns. Even the
receiver is guaranteed inaudible at 2V for 98dB horns at 2 volts!
Once you've got the high gain mode quiet enough, keeping going just doesn't do much for any real-world use case. The limitations are always upstream, and even then they're almost always just fine in high gain too! You'll almost never need the gain control to put
more than 2V into the unit. The only place you conceivably might use it is to "size down" the amplifier even more, so that 2V gets you 10W output (with very sensitive speakers), and allows you more range on the volume knob and to maximize pre-amp SNR at 2V. Essentially you're then turning it into a 10W amp and readjusting your gain staging so that the amp continues to put out the desired output with a 2V input.
