Hi Denis,
The placement of the notification pop-up is purely a matter of personal preference. I like it near the top middle of the display screen. Of course you as the designer are free to put it where-ever you want and allow for adjustment of the position or not. Some of the other modern skins I use default to the top left corner and allow enough pixels to be added to the x and y coordinates so that the pop-up could end up in the bottom right corner (or almost anywhere) . The default Winamp modern skin placed it in the bottom right corner (with no way to move it). Being able to move the current top middle position a little further down and to the left would be nice for me (since the pop-up expands or shrinks depending on the info displayed), but the current position is good enough. Being able to move it a little further from the corners might be useful for others. Some notification pop-ups are a fixed size and truncate info that doesn't fit. I like the way yours works much better.
Stereo Tool is a great sound enhancer. But it does have a 'ton' of options. It took me weeks to finally get it setup the way I liked. Something that works well across the various genres I listen to. I also have a few setups (presets) tailored for specific cases. It's kind of hard to find one group of settings for everything. My goal was to clearly hear everything (vocal and instruments) even at low volumes. I've found that small adjustments work better than large ones. Make a change and listen for awhile (2 or 3 songs) to give your ears time to adapt. Then decide if you need more or less of the adjustment. You can also get presets from the Stereo Tool forum to try.
As for the latest version of your skin, you've made some great additions, imo. The 2 analog VU meters view is a nice one, even though it doesn't really show the bass and treble variations in a song. I like the single analog VU meter view. The bitrate and file format info now updates correctly when the song changes. I also discovered something related to the timer mode reverting to time elapsed with each song change. The classic skins in my collection were set to show elapsed time. When I changed them to show time remaining, your skin also stayed in time remaining mode. I don't know why the classic skin setting affects your modern skin this way. The other modern skins I use don't care what the classic skin settings are. All classic skins use the same set of settings. Modern skins usually can be setup individually.