...the same is with pictures resolution 1080 p picture will look better and a bit sharper on 4K TV instead full hd TV with the same resolution
This is not something you want to get into with me. I know televisions fairly well. This assumption is not just wrong, is is blatantly wrong.
Upconversion of a video source is highly depending on the video processing which is in use and the display it is being fed to. Quite often the display and the conversion chip are significantly more modern. So, they have many intrinsic advantages which allow for minimal artifacts when converting from 1080p to 4K, but minimal artifacts is not the same thing as NO artifacts. The real advantage of that 4K display comes from it simply being a more modern piece of hardware, which may have better technology used in the display that already makes it brighter and have better or more accurate color saturation vs. an older 1080p display.
With front projection I see this all the time where people are thrilled with their new 4K projector, when watching 4K/HDR content, but for the most part, they see no difference between their older 1080p projector, and the brand new 4K model. Sometimes, they see a drop in contrast and complain that the experience is worse.
The bottom line is that you are making assumptions, and that's not the way this works. The individual product may do a great job with upconversion and may deliver a very slightly improved output, but it won't be completely free of artifacts introduced by the algorithm in error. At the end of the day, those chips are guessing at how to fill in the information, it's not dealing with an actual 4K (or high audio sampling) rate. So, there can be unintended errors in some content which would not be there if the original source was played back exactly as it is presented on the disc.
This is not the same as higher resolution/bandwidth content. That content starts out with more to work with and will inherently be better, or at least more accurate, from start to finish. It is what should be used, at all times, if best audio quality is the goal. This also means that appropriate equipment is in use to deliver that content.