I use the CEP system with my flight helmet (HGU-55), but not with headsets. I also use Oregon Aero kits for liner, earseals, etc, for improved noise attenuation.

I use Bose headsets, usually no ear plugs. In exceptionally loud aircraft where a headset is worn, I may use passive headsets with Oregon Aero hush kits (extra foam, better noise attenuation), and ear plugs beneath. There does come a point of diminishing returns when one needs to turn the volume up loud.

For earplugs, I carry Radians custom molded plugs. You mold them yourself. In lieu of those! The foam expandable in-ear plugs are hard to beat.