A good question. Not sure if my answers will be any more useful than the others you have found but for starters, qi is
interesting and qi is
mysterious. Interesting because it is so unexpected and subtle - when I first started noticing it, I was quite surprised to find that it existed - even though I was taking a qi gong class at the time. And it is interesting because there are so many different ways to explore it and play with it. Mysterious because even though we talk about it, manipulate it, employ it - you can never really locate it or say exactly what it is - more an experience than a thing.
even tactile sensations are clearly flowing; also, listening to music makes me feel distinct, flowing sensations associated with notes; emotions are flowing too; are thoose stuff "qi" as well?
Could be. I think of emotions (pain also) as compounded - kind of a pattern of energy that gets locked-in by a mental overlay - like a sand castle getting sprayed with epoxy. If you were to relax more into these sensations you might find them composed or made up from a more universal elemental kind of phenomena - that I think of as the qi. So you can investigate these things and see what happens. On the other hand, sensations of warmth, coolness, tingling and the like are good sort of gateway sensations to work with as you get a sense of the qi.
Also, I came across the concepts of "refining qi", "different kinds of qi" or "turning qi into shen", and the like.
In my experience, it seems to relate in this way: there are flows associated with the breath (and with every other physical moviment, for what matters); in the beginning, they feel like flowing pressure; after a while, they change and they begin to look transparent, or luminous, (sorry, don't know how else to describe it) or golden, and when they are like that, that feels so much better. Is that what is meant by "refining qi", and "different kinds of qi"?
I think that is an aspect of that process - one way it manifests. Taoist Internal Alchemy is one of the ways that people have come up with to work with and understand this phenomena. They really dug into this stuff deeply and have some great techniques - as well as some of the most cryptic (though very cool) symbolism around for talking about it. Traditionally, the refinement process takes place through working with specific channels and centers.
What you might be describing is how when an area first opens up - the movement of the energy can be kind of course and/or restricted then over time as things open up more it takes on a more pleasant, kind of warm flowing or even field like feeling that can be very pleasant - so pleasant that our awareness can become quite absorbed in these sensations. Personally, I would put this also in the realm of 'refining qi' but not sure if others would.
Another possibility is that it seems that all different kinds or flavors of energy can get kind of buried in the body and as you work with this stuff you can end up releasing these things - they can be anywhere from quite blissful to very painful but don't usually last very long.
And yet another possibility is that you are just sort of relaxing into the process more. As you do that, the quality of the sensations may kind of morph as you become more sensitive - also perception can play a big role here too as how you feel these things can be shaped very much by your intention/perception - this is actually a very important skill to cultivate.
BTW, I make no claims to being a Qi Gong Master - a nescient taoist - at best.
Take care and happy cultivating
