I ordered KSC75 replacement speaker units from China, along with a pair of pads, for my Sena SRL2. They're on the way.
The parts on the way
The replacement speaker units I ordered, pictured in the seller's listing.
I'm starting with the replacement units rather than taking apart a complete pair of headphones.
The replacement pads I ordered.
Why KSC75s?
There's a good example in Sena's SRL2 speaker-upgrade discussion. Simon Bowen fitted a pair of Koss KSC75s into the Sena setup in his Shoei Neotec. He removed the ear clips, joined the wiring, kept the microphone connection working, and held the new speakers in place with Velcro.
Bowen reported much better bass and volume. Another rider, Adrian Duckenfield, later tried the same idea and also liked the result. That's the sort of small upgrade I want to try with mine.
I'm mostly interested in what the swap does for music and voices inside the helmet.
Next step
When the package arrives, I'll work out the mounting and wiring and take pictures along the way. Then I'll come back with how it fits and sounds.