SFX Volume issue
The volume for some SFX are too loud compared to other sounds such as character voices and other SFX. This is normally not a problem because you can change voice and SFX sounds individually. However, there are some SFX sounds that are quiet and others that are very loud, so if you really want to hear one sound you have to deal with the others blasting. I usually put my character's voice on 100 and SFX on 20 (in game volume) just as an example of how great this difference is. I believe there's two different solutions here, one: the volume for certain "quiet" SFX's should be brought up (or louder ones brought down) or 2: Create an equalization option for SFX specifically (could also make one for all sound in general). I think this second option will probably be much easier than individually going through each sound to see if it's too loud or too quiet.
I noticed this specifically doing Mordekaiser's dance where he plays his guitar. I love hearing the guitar being at great volume but then the other SFX sounds are too loud (his W and ult especially). I think this could also be fixed by putting his guitar in the "voice" category instead.