Yes, it's exactly the same with me.
But don't give up. ...
I have thought about it again and would like to contradict myself a little.
I think I found a solution now. And no additional configuration option would be needed.
And what I am thinking about would be very simple to use.
As you have probably seen in my script, files and directories are being read recursively. That means You are free what directory tree structure You use.
When Image files are chosen randomly, I can determine in what parent-directory it was found and than try to scan for a similar sub-directory within the sound file tree and let a sound file be chosen from there and otherwise from the entire collection.
That means You can than arrange Your image files and sound files accordingly. And You can do a mixture of both.
And as image files are chosen randomly the surprise effect will remain (kind of).
It's up to You then, how You fill the sub-directories that will lead to medium lvl sound files or high lvl sound files a.s.o.
If You are using linux or mac, you don't need to copy files. You can just throw in links as You like and change that when ever You want.
How does this sound to You?
This could be enhanced later on by randomly chosen mapping rules, so that for instance the sound directory containing lvl "1" files, today is matched when images from your theme "3" are shown and tomorrow a completely different mapping can happen. So if the sub-directory names are simply digits for instance, even a time dependent rule could apply.
Please, think about it and let me know what you think.