I have to agree with the OP.
I also suffer from Migraines, Cluster Migraines, Cluster headaches, and Sinus Headaches.
And, even when I am not having a migraine, the Trainer Activated sound is very very loud.
But, I used to have 5.1 speakers like that, and I just turned the sound down on it, then launched the trainer, then launched the game, then activated.
I would then also get the VERY loud sounds of up to 9 Activated sounds. Plus all of the Deactivated and Trainer Deactivated sounds when you deactivate a setting, or control plus h to deactivate the whole trainer, then activate it again and reactivate everything else, for those times when a game needs to be Deactivated for reasons of the game picking up that something is wrong, or the trainer stops working and a deactivate then activate fixes it.
This is harder to control ingame then just the speakers, as each game has its own sound level.
And, while I VERY much appreciate the Mute function, that I just learned about right now, it doesnt help because sometimes you have to press a button 2 times to get the Activated message. In other words, we NEED to be able to hear when its activated or deactivated, all the times it does it, otherwise we might walk into a situation where the trainer or certain setting is just not on.
But, I also get that you cant go back to old trainers to do this.
Maybe with new trainers you guys n gals make?
Or, the OP can do what I did, and buy a wireless headset. Corsair makes some very good ones, with very little lag, good sound, and cheaper than most premium headsets. And, they usually have a LARGE scroll wheel on them to turn the sound down, the back up, very fast its the reason I stick with Corsair, the large button for volume. I can just barely move my hand to make it less loud, then after everything is activated, I can barely move my hand to make it louder.
Also, at the OP, you should not be playing games when you have any type of migraine. It makes it worse 98% of the time unless motion or light sensitivity isnt triggered. Usually a dark room, turn the AC up to make it cold, a cold pack on the eye, or eyes, or head, where the pain is most. Or, a very hot shower with the door closed so there is a lot of steam. The longer you can stay in the steam the better. And, Imitrex or even better MaxAlt-MLT. The MLT version you put under your tongue so it works faster than any other migraine pill, works well to try to stem the tide. I know. I can be down for 3 days because of a migraine, or cluster. They are terrible.
Anywho, signing off. But I do support making the sound just a tiny bit less loud.