how to use gain control on a preamp


Maybe a silly question, but I just got a Magus preamp, paired it with a Belles 150a SS power amp and find it a bit bright with my speakers. Fellow who sold me the Magus said keep the right and left gain controls wide open. This doesn't work--too harsh in the highs. So I pull back on the gain and it keeps the detail, but where is the optimum?

I feel like I could fiddle back and forth with the 3 controls for quite a while before tame this beast. There are also gain controls on the speakers which has always been a problem figuring out. I try to keep that sort of in the middle (30 yr old Chicago Speakerworks 2-ways). Of course I should put some carpet on the wood floor and drapes up to calm things down too.

Well just wondering if there is some sensible process to follow so I don't wander around in the gain control wilderness.
lynnc
i had an early belles amp, with the same pre (bought from House Of Hi Fi in St Paul). had the gain set at 3'o'clock..not open. played incredibly on celestion , chapman and several others. the room interaction (which you've noted)will dictate your final position.
I remember using the Gain and Volume settings on my Audio Research Sp 11 and found that I had the Gain setting at about 75% and used the Volume only after setting Gain..I also remember the older Audio Research Preamp units were supposed to sound better with the Volume at a higher setting,so I moved the Gain control lower to get the Volume control to aprox 12 o'clock high ( normal listening level ) ..Can't really say it makes any difference but I would suggest just set it and forget it....Not sure if that helps but????
If memory serves, I set the left/right gain so that the normal listening range of the volume knob falls in the 10:00 to 2:00 position.