Infirmations about audioresearch LS 26 "Gain"

On an audioresearch LS 26 preamp, how does the LOW- MED- HIGH « Gain » affect the sound ?

Probably the use of the gain is to balance the out put of different source for exemple phono stage vs CD player.

But, is there a best « Gain »position to obtain best sound ?

Looks like on Low gain the sound is softer, and on High gain more detailed sound

Is High gain make the power amp work in a more Class A mode?

Would it be it a sort of resistance, that make the LOW- MED gain functionning?

Or is there kind of booster for the High gain ?

If the LS 26 have "No gain mode", (Defeat mode) which one Gain would be use (heard) ?

Thanks