Sybe07 said “My impression is, in this way it can be understood that the vinnana that sees, hears, smells etc. is a kamma-vipaka. This vipaka is just neutral, not moral or immoral.”
In my opinion, all initial sense inputs are neutral and due to our karmic essence as humans and appear in kamaloka, these are bound to come in front of us. What to do with those inputs creates a good or bad deed in future which might be next moment as a continuity.
Also it is right that nothing appears without reason and those happen due to kamma vipaka be it neutral, sukha or dukkha, immoral / moral.
Sybe07, I tend to agree with you that initial inputs of vinnana as in seeing, touching, hearing, smelling etc., are not only due to kamma-vipaka but also are neutral.
If we were to deeply penetrate, then as an experience can get to a stage that the vibrations / feelings which are got through move from being neutral to either becoming good or bad feeling based upon gati which is defined by kamma-vipaka. From the neutral inputs, if one were to not take any action, then it drops away and does not appear again. This is equal to saying that everything arises, stays and drops away and nothing is there in true sense to be called as “solid experience”