You are in a difficult position protecting the hearing you have while accommodating your need to hear on the job can be tough. Earmuffs achieve their protection from noise by sealing completely around the outside of the pinna, or outer ear. An extender as you describe would most likely break the seal around the outside of the pinna and make the earmuffs ineffective. The cushions on most of these devices are soft enough to accommodate safety glass frames without breaking the acoustic seal, but be careful. The simplest way to test these devices is to simply listen to noise with the muff in place as you use it along with your safety glasses and other equipment, then lift it off. If you dont hear a significant difference in sound between the muff on and muff off conditions, its likely that the muff is not doing you much good.
Your approach of using hearing protectors in conjunction with your hearing aids is generally very good. Here are a couple of ideas that may help.
Can you get enough volume (gain or output) from the Peltor Tactical Pro devices you use now to enable you to hear without your hearing aids? Most of these sound resoration hearing protection devices have volume controls and can provide up to 80-82 dB output. That might that be enough to permit you to hear without your BTE aids in place.
- While the Peltor device is very good at what it does, it has a relatively small earcup. You may want to investigate getting the same sound restoration technology in a device with a larger earcup to provide room for your BTE aid to reside comfortably. Peltor has other models of earmuff with similar technology, and other manufacturers like Bilsom (the Targo and 707), Howard Leight (Thunder and Leightning models), and others manufacture devices that may meet your needs.
Its important to keep in mind that hearing aids are not designed to be used as hearing protectors. In many cases, hearing aids are vented, allowing noise to come in from the outside. An approach like yours, to use your aids in conjunction with hearing protectors, or using hearing protectors that may be able to substitute for hearing aids, are the safest way to protect your hearing and maintain your ability to communicate.