My experience is that indoor versus outdoor shooting makes a difference. Outdoors I use electronic plugs rahter than muffs, and they work fine. Indoors I use quality passive plugs with electronic muffs. Wearing muffs and plugs together really helps, but inderstand that the NRR ratings are not additive. Rather, the second protectors add only about 5 NRR to the number on the higher rated of the two.
Also, there is a difference between electronic noise-cancelling earphones, which are really nice on airplanes and computer server rooms, and shooters' electronic muffs. Noise-cancelling earphones continually "hear" outside noise like server fans, manufacturing site noise, or jet engine rumble and produce a 180 degree out-of-phase noise to cancel that sound, while still allowing most mid-frequency sounds from outside to rech you , only muffled by the phsycial padding around the ear. Frustratingly for the tech-aware, descriptions of noise-cancelling earphones rarely tell you the frequency ranges and amount of counter-noise they cover. Remember, they are designed to enhance the quality stereo sound they deliver from your phone or iPod, while blocking intrusive or harmful levels of outside noise.
In contrast, electronic hearing protection for shooters, whether plugs or muffs, have microphones on the outside delivering outside sound to you ears controlled by the volume control, but when they hear the crack of a gunshot at a high decibel level, usually about 80, their electronics very rapidly shuts off the speakers momentarily, so that you get the full protection of the physical block from the muff or plugs. This means the actual noise protection comes from the physical padding or plug, not any electronics. This also means you want the plugs well positioned in you rear, o rmufss with quality padding and protection. The electronics are there to help you hear conversation and range instructions, but chop off the sharp gunshot crack. As noted above, if you get ones with bluetooth they do help with hearing telephone or music.
I have been trying to find if there are actual noise-cancelling protectors for shooters, that use the 180 degree noise method to negate the gunshot sound, but so far have not discovered if such a product exists. If anyonie is aware of such a product please let us know here.