Done! I have pictures!
This is the product I ordered.
Grab the cushioned part by the edges and twist back and forth till it breaks the internal mount loose.
The mount that breaks is just the center post.
The back of the speaker is oddly shaped. In order to get a usable surface for mounting, I clipped the post and bridge, then filed the plastic smooth.
I used some glue-backed Velcro.
The new units are about 3mm larger in diameter and about the same increase in depth.... But the cone shape fits the Shoei's dished cutout better than the flat-bottom Sena speakers so the net change in height is about nil in this helmet. The larger diameter is also not an issue because the outer edge is wafer-thin and the Shoei dished area opens up pretty well.
The wire used in the Sena units is much more robust than what's used in the Koss. Just clip the wire right at the Sena speakers and solder straight to the mounts on the Koss speakers.
The Shoei makes it easy with its removable liner.
The best part is the sound. Now, I haven't had a ride test yet but the difference in sound quality is outstanding right away. These little speakers have something the Senas never had...bass!
This is definitely a great upgrade and I'll find out soon how well they work out when riding.