Dear Jochen,
Good to see you, and thank you for the careful reading of my essay.
> I think you may want to accept the first thesis---your S essentially being the intrinsic properties grounding the relational mathematical structure of P
By S I mean the "speakable" related to sentience, but not sentience itself. Sentience is the ontology of S. I find that the most natural solution is S=P.
> I think the resulting panpsychism or pan-experientialism faces some difficult challenges, such as the notorious combination problem.
I think the same. I think S=P is like pan-experientialism, but I don't think it faces the combination problem, because I don't think there are separate units of sentience, rather sentience is the ontology of both S and P (is this different from "grounding our models"?). I think fundamental sentience faces another problem, which I called "the climbing problem" in my extended essay The negative way to sentience. But, while this is a problem, it allows Hypothesis 1 to make empirical predictions and be falsifiable, which I think it's a good thing.
> if two people are led to similar views along independent routes, one just might hope that there's something worthwhile to find at that destination
Indeed, this qualifies as "intersubjective verification", which I mentioned in "The negative way to sentience". If you have comments, I look forward to hear them, no matter if you disagree, I have this on ResearchGate with the words "comments welcome" in the title, since I'm still collecting feedback. At the same time, I'm looking forward to read yours, and I expect, based on your previous ones, that I will love it.
Cheers,
Cristi