I have a Nolan N103 modular with J&M top of the line speakers I installed.
When I first put them in, I took the liner all apart, spent some time with an exacto knife and put them in. The Nolan had "ear pockets" and a "valley" for the wires so it went pretty good.
I tried them out first on a ~400 mile RT route with a friend of mine and my ears hurt so bad that it was all I could do to put the helmet back on/take it off at gas stops!
So, I went back and pulled it all out, then started cutting again. The exacto/razor knife wasn't gettin' it, so I took a sanding disc on an air/rotary tool. I had to cut down the diameter of the sanding disc, but it worked great to get the area down to sink the speakers in better.
I have since worn this helmet for thousands of miles with no issues. The moral of the story is to sink them in enough and ride progressively longer routes until you're sure they won't make them ears all tender.
I have installed speakers in two other helmets; the last one before the Nolan was a HJC modular (don't know the model# right now) and didn't have the same problem. The Nolan fits really well in all other respects, so it's something to do with how the cheekpads/side of head where the speakers go that is different.