Now that is exciting!
There is something I would love to sort out here: my understanding was that the jumpers would let you choose the gain of the buffer, from 0dB (13dB total) to 13dB (26dB total).
But now looking at your photo the markings on the PCB indicate "buffered/unbuffered", which is somewhat different from a simple gain change. The manual states this is a bypass option, which is confusing again: does it bypass the gain stage or the whole buffer, in which case the input impedance would be quite low...
Can't say. The EVAL1 document says this is a bypass of the FE gain stage, resulting in 0dB gain from the FE. However, there are no input impedance specs listed at all (let alone in both configurations) to confirm whether the 0dB setting gets you a unity gain buffer, or a true bypass. It might be possible to "ohm it out", but that is not something I can get into for a while.
Given the purpose of the board, to facilitate evaluation and development, I would expect that it does indeed bypass the buffer gain stage. Hopefully, others will find the answer without resorting to tracing the circuit.
Personally, I expect to be using the buffer gain stage, but I might want to dial down the gain to 6dB or so. TBD.
Since this simple photo already triggered new questions, perhaps I should take a better photo of each of the two production board types and post them here.
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January 6, 2020. New information here:
https://www.audiosciencereview.com/...iy-purifi-amp-builds.10478/page-8#post-296652