Like I say, "gain maxed out". Which is obviously very ambiguous.
I would have to look up the specs on a Parasound 1206 and an Emo USP-1.
If I'm going DIY, I would tend to choose my parts to shoot towards the low end of the normal gain range. Likely target a gain of 27dB to 29dB. And, I make that choice based on the exact items that we are discussing here.
However, if I know that my source may need the extra gain to drive an amp to full output, then I may choose 32dB. I likely would not ever plan to go much higher than that though.
Adding a high quality Alps pot for DIY is likely gonna cost something like $12, and in that case it may be worth designing on the high end and know that you have the luxury to attenuate it if you need to.
I also thought 32 dB gain is a little too high, unless there is a good reason for it. My first DIY amp (would consider it dead silent too) has very low gain, the Nelson Pass 5 W amp. I just order the kit for the 25 W F5, that obviously has higher gain, but hopefully it will still be quiet.
One thing I should have mentioned too is the sensitivity of the speakers. A 100 dB/2.83V/1M Klipsch is going to be more prone to hiss than a 84.5 dB/2.83V/1m Dennis Murphy's BMR.
To summarize, at the minimum, one has to consider the following, and I am not talking about ground loop induces noise, or transformer hum.
- speaker sensitivity
- length of wires
- path of wires,
- amp gain
- amp internal layout
- amp components that could be sources of noise, such as resistors.
Noise is such a complicated issues, fortunately there are too may noisy amps out there any more. I have so many of them, and none has any sort of noise that is audible from a few inches away, even when the room is in its quietest moment.