I don't really know how to answer the things that came up

Si is basically a parallel sensory experience running alongside with the outer experience, being attached to it. I see a tree, visually, but it always comes together with the additional introverted component (Si).

This introverted component is hard to describe, but good candidates for descriptions are words as: organic, genuine, old, patina, sensory depth, (see Jung)

This is what Socionics is referring to when they describe Si as "aesthetics".