Ciao, thanks for the comment.
The export typically takes place by specifying a memory address and possibly other parameters such as the locations to be used in page zero: this is what the most famous music trackers (such as Goat Tracker) do and if you are using one, you certainly already had to reserve a memory area for the music (moreover aligned to 256 bytes, a limit that my tool does not have). Honestly, I don't think it's a big deal.
Yes, it's true that the IRQ routine is already present in the exported code, but it's more useful for those who use it in BASIC. The goal of the displayed assembly code is to show how to put the play routine inside your IRQ code (usually you just want to add the sound effects to an already existing IRQ routine). And yes, not all the addresses for the other routines were showed, but again the goal was just to show an example of use in assembly.
I didn't notice the stop button bug, I'll fix it.
As for the problem with high density screens, I've never noticed this because my screen is full-hd. I need to find a way to test it on my low definition monitor.