As you would expect, too much gain not only makes it difficult to make fine adjustments to the volume, it also makes whatever noise you might have more troublesome. I don't know if using a lower impedance CF will have any effect on that or not. I've never associated lower impedance with noise reduction but, again, I'm not that well informed.
From an impedance matching standpoint, the output from a DAC should be low enough that it will work well even with an amp that has an input impedance of 10k. So impedance matching shouldn't be an issue with either amp. DACs don't have gain, as far as I know, so it's not contributing to the gain problem. And I don't think that the digital output from a computer adds gain either.
So the gain / sensitivity issue seems to be inherent in the amp design. I'm totally ignorant when it comes to SS amp circuits. But a tube amp with a very high gain input tube (or too many gain stages prior to the output tubes) might exhibit the same symptoms - a very touchy / limited range of adjustment on the volume control and increased sensitivity to whatever amount of noise might be coming from the source.
That would seem to point to whatever is analogous to a "high gain input tube" in a SS design. If the amp is too sensitive you can either modify the amp (like using a lower gain input tube) or you can attenuate the signal significantly before it gets to the input of the amp.
Since you seem determined to resurrect your dormant preamp and turn it into a CF, there's certainly no harm in trying it. Only you can decide if it actually provides any audible improvement and if the any increase in SQ is worth the added complexity.
I just don't think that a CF alone will solve your gain problem. A voltage divider can and it seems like it will be necessary to add one regardless of whether or not you add a CF. Either that or modify the amp in some way that results in it being much less sensitive.
The CF comes after a volume control at the input, which is a voltage divider. My DAC, like most others, doesn’t have a volume control, and puts out a full power signal all the time. It doesn’t matter what the computer is feeding the DAC with respect to signal strength. The signal level may be low due to reduced volume from the PC’s volume control, but any residual noise from the PC is constant. At least in my case it is. Increasing or decreasing the volume on the PC has no effect on the noise level coming from the speakers. I will also try a simple pot at the input of the amp.
I believe many CD players, and many outboard DACs put out about 2.1Vrms at full scale (3V peak).
If the music level is recorded at -20dB full scale instead of 0dB full scale (I have some CDs with both those recorded levels) -20dB full scale is 0.21Vrms, and 0.3V peak.
If you have 20dB "extra" gain in your system, then a volume control allows you to turn-down the 3V peaks, and to turn-up the 0.3V peak of different recordings.
That way, you can set the volume control to have the same maximum volume out of your speakers, in spite of those 2 different recording levels.
If you are hearing noise from a playback system that only has a DAC, integrated amp / or power amp, and speakers, then it is most likely that:
Your speakers are very sensitive
Your ear is very close to the speakers
Your integrated amplifier / power amplifier needs to be repaired / re-designed.
If the music level is recorded at -20dB full scale instead of 0dB full scale (I have some CDs with both those recorded levels) -20dB full scale is 0.21Vrms, and 0.3V peak.
If you have 20dB "extra" gain in your system, then a volume control allows you to turn-down the 3V peaks, and to turn-up the 0.3V peak of different recordings.
That way, you can set the volume control to have the same maximum volume out of your speakers, in spite of those 2 different recording levels.
If you are hearing noise from a playback system that only has a DAC, integrated amp / or power amp, and speakers, then it is most likely that:
Your speakers are very sensitive
Your ear is very close to the speakers
Your integrated amplifier / power amplifier needs to be repaired / re-designed.
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My speakers are very sensitive at 104 DB/W/M. My ear isn’t very close to the speakers at about 8’, but my room is very quiet as it was purpose built for audio and well insulated from outside sound. The amp I am having problems with os a DIY Aleph J with very low noise with shorted inputs.