Sena I am BEGGING you -- please find a way to support "bone conduction" technology, so I can wear earplugs and still use my Sena. I will even buy a new Sena if you can build a solution. There are a few easy ways to create this:

1. Offer transducers instead of speakers that attach to my helmet checkpads. You'll probably need a bigger battery to drive the transducers, but this works great. I currently do this with a hardwired Aftershokz headset plugged into the Sena speaker jack. But it's really uncomfortable in my helmet, it requires it's own battery, lots of extra wires, and is a PITA.
2. Partner with Aftershokz, and have them build a helmet compatible transducer accessory that works with Sena output jacks.
3. This third option isn't great, but you could build a Sena that has bluetooth output. This would allow output to a wireless Aftershokz headset. It would still be uncomfortable under a helmet, but at least it's less wires to worry about.

I hate those foam hearing protecters with speakers built in, btw. They typically don't offer enough hearing protection, the quality is awful, and the foam breaks down after a few uses, just like regular foam hearing protectors.