Michael, that’s probably because you are mostly using TOTL DAPs.
![Headphone Smile :) :)](https://cdn.head-fi.org/e/headfi/smily_headphones1.gif)
In terms of driving IEMs, the improvement from adding C9 is definitely smaller if you pair it with something like P6 Pro, compared to when you pair it with mid-tier DAPs like LP6K or R6.
Basically, if we agree that there is a difference between mid-tier DAPs and TOTL DAPs in their ability in driving IEMs, then C9 shall be a (potentially) useful improvement to the audio chain.
Edit: To quickly add, C9 is definitely doing something very noticeable to my N6ii (E02). My reference point is Hugo 2. N6ii is nowhere near Hugo 2 without C9. With C9, it becomes at least a draw to me with my various IEMs. Of course, we can talk about whether this is due to synergy or other things, but I just want to point out that, to me, the improvement it has for mid-tier DAPs is genuinely there.