You should put the gain control on your sub at half way and use the Marantz supplied microphone calibration system, Audyssey, to determine what works best for that particular room shape and sub placement. As long as the value it determines is not pegged off scale (that is, +12 dB or -12 dB) then that gain setting on the sub's amp is good to go. [Although some people like to tweak this level slightly, after it has been determine by measurement, to suit personal taste.]
There's a lot of audio mythology out there, including in this forum, that certain sub output level values work better than others perhaps based on very early subs made in the 1970/80's which didn't have as much latitude in terms of what levels they could easily accommodate, but with modern designs this shouldn't be a problem as long as you are not pegged off scale, like I just warned about.
In A/V reproduction accuracy, there IS no concept of "accounting for personal taste/preference". As art consumers we don't "pick" the level of bass, nor the tint/brightness of a scene's sky, any more than we pick the ending of a novel or Mona Lisa's type of smile. "High fidelity" means "high truthfulness", faithful to the original artist's intent: an unmodified, neutral, accurate copy of the original master, ideally being exact and with no discernable alterations, aka "transparency".
Last edited by m. zillch; 07-02-2016 at 08:25 AM.