Upload & Sell: On
I can empathize.
To me the Holy Grail of brown toning is illustrated in LensWork. A deep, rich, but not overly saturated chocolatey brown. Is that what you seek? Have you been able to find an example and check out the RBG values over several areas?
My efforts usually take me to setting hue around 35-38, balanced heavily for dark tones over light, and keeping the saturation pretty low.
Love to hear what others have come up with.
But, if you have permission, post an example of what you are trying to emulate, or post a link, assuming you are talking about a non-print rendition that works for you.