Which frequency to adjust if voices/mids give me a headache.

I think I found a decent solution for the moment. 

As I mentioned I had the Lintons and the 4.2s.  I did room correction for both.  It turns out I really like the room correction for the 4.2 applied to the Linton speakers.  Goofy, I know but I'm pretty happy right now.  I also pointed the speakers straight ahead and that helps a bit. 

It turns out I really like the room correction for the 4.2 applied to the Linton speakers.  Goofy, I know but I'm pretty happy right now

Put 4 inch absorptive GIK panels on the ipsilateral and contralateral reflection points on both side walls. If you’re sitting crack up near the back wall, treat it too.

It can give more happiness (than right now) and reduce the headaches even more!!

An all-too-common problem in recordings is vocal sibilance, typically cause by using the wrong microphone or having it placed too close to the singer's mouth -- we want to hear them sing, not examine their tonsils.  And, there are some singers who just naturally have a more sibilant quality in their voice.

This is a very difficult problem to fix once it is in the recording itself, though some audio systems may emphasize it more than others. If you have EQ available, try reducing the level on the 5KHz to 8KHz band and see if that helps.

As a musician, most singers ARE a headache.