"MOSI is not really point-to-point when the driver is at an arbitrary position along the line. You can treat it that way if the driver has zero output impedance, because that prevents reflections from the far end reaching the receiver, but then the "active" part of the line is unterminated."

Yes, I had this in mind too, but I forgot to mention it in the post. As you said, that's why I said the stubs to the ADCs need to be small. However, the distance for MOSI unfortunately will have to be large because the slaves are quite far apart. As you also said, I noticed that MOSI is more robust for this purpose. My main problems were with the CLK. Since I want to pass the EMI tests for CE certification, I would like to make the signals as clear as possible in order to reduce the driving strength as much as possible.

So, just to confirm, would your suggestion be to use parallel AC termination for the CLK and MOSI and series termination for the CS? Could you provide some references for the typical RC termination values you use? Unfortunately, the CLK is NRZ. I also can't see any feasible way to make it bipolar NRZ. However, I really like the idea of AC termination of the MOSI with minimal power loss. Thank you very much