Mark Levinson 326s

I own a Reference 32 preamp (same as 326, except with power supply in a separate box). I did not do any sort of rigorous testing so I cannot say if any particular setting is the "best." I don't think that the different choices reflect actual differences in the number of gain stages the signal goes through, so the choice of 6db vs. 18db merely reflects the amount of attenuation applied to the signal. With the logic circuit employed by ML to control volume, no matter what one chooses for rough gain setting, volume and balance, the logic circuit switches in the appropriate combination of resistors and minimizes the number or resistors used to achieve the particular chosen level. I would expect there to be minimal differences between choices. If you pick higher gain and then use the lower part of the volume control range you should get the same result as picking lower overall gain and higher volume level settings--for any give volume it will be the same combination of resistors chosen by the logic circuit.

Personally, I would pick an overall gain level that keeps the volume level control in the range where each level change is a .1db step. I also use the preamp's ability to change the gain individually for each input so I can roughly match the volume level from various sources. I use the maximum volume feature to prevent accidents that would result in way too high a volume level being fed to the amps.

This is an amazingly versatile and controllable component--just don't drop that heavy remote on your foot.

I have kept my 326S set at 0db for inputs 1-3 which I believe is the factory default setting. I listen to mostly jazz at medium volumes and at this setting I can keep my volume control between 4 and 5 listening to either my ML512 or McIntosh MR88 satellite tuner.

I own the 326S as well and I can tell you the sonics will change based on the gain settings. 0-6-12-18db are selectable. Going to my McIntosh MC 402, 9 gain sounds thin and lacks dynamics 6db of gain brings out more body and dynamics, and bottom end, going to 12db of gain really adds much more of what the 6db setting does, 18db of gain is overripe and to warm. So they all make a sonic impact, so try them, I stay with 6db of gain but at times I like the 12db of gain, the 0 & 18 dB of gain sound the worst. 

Update. I purchased the matching ML 532H amp. What I can say about gain is the improvement it can make to your system. I have an ML amp and 326S preamp, and I can set the preamp to o gain, 6db, 12db, and 18db. Each step up from zero improves the sound, I like the 12db, but I recently tried the 18Db, and what I have experienced is a more relaxed sound, more open, more dynamics in the bottom end, and just a more pleasant and natural sound without any downsides. 12Bd sounds more sharper and detailed but not as natural as the 18db, So gain does make a sonic impact which is why buying a new preamp with more gain than you had before will sound different for sure and most likely better. My vocals are now in the room with body and openness. I guess much less like a recording.