Coming into this late but the first thing you need to do is differentiate between gain and attenuation. Gain is fixed at 18dB and attenuation is variable.
The 800 pound gorilla in the corner is lumping gain and attenuation into an arbitrary setting of a dial without reference.
A decade ago I measured some flavor of the day 10K pot to relate the gain to rotation in both dB and voltage ratio. By no means is this a standard, it is just a statistical sample of one but hopefully it illustrates the issue. (remember these values are for attenuation only)
(Apologies the formatting doesn't hold it is a three column table)
Rotation Db attenuation voltage ratio
7.00.00 AM 0ff NA
8.00.00 AM -50.798242 400
9.00.00 AM -37.669889 78.78787879
10.00.00 AM -28.995433 28.10810811
11.00.00 AM -21.98006 12.14953271
12.00.00 PM -13.492213 4.727272727
1.00.00 PM -8.299467 2.524271845
2.00.00 PM -5.2231697 1.818181818
3.00.00 PM -2.7932399 1.382978723
4.00.00 PM -0.7861947 1.06122449
5.00.00 PM -0 1
This is where it gets fuzzy without the actual numbers of "your" attenuator wrt "clock rotation" If we make the grand leap and assume all attenuators have this particular taper, it becomes easy.
With 18dB of gain, you would have overall unity gain between 11 and 12. (again assuming you have the attenuator I measured installed) This means if you listen at 1-2 the concept of a passive is really not an option since you would actually need gain. (again look back at the assumptions in this story)
Unfortunately there is no bureau of standards for the audio industry so you have either have to roll with it or put in the time to learn some of the basics to make an informed decision.
My gut feel is adding more gain to simply add more attenuation is not the way to go.
It is also important to realize I have only addresses the gain aspect of this situation. There are two other key points that play a more important role in system synergy which are impedance matching and headroom. Unfortunately neither of them can be directly read by the dial rotation value.
dave
