You asked, so i will answer,
Nuprime designs their own patented Class D circuits, Orchard Audio (maybe you helped?) has new GaN jobbies, Merrill Audio has their own GaN jobbies, AGD has their own GaN based Jobbies, Lyndorf (and the original TACT amp) design their own circuits and I have seen several others I cannot remember. There are two more GaN based in house designed amps about to hit the market ($1600 Class D Audio/Premium-audio brand and the $2500 LSA Voyager). Most other companies use stock or modified modules from the big 3 (Pascal, UCD, IcePower).....and add their own front end and sometimes power supply to them.
And then some of us tweak whatever we can to improve the sound. You don't need to know how to design something to improve the sound.....as every little thing you do can change the sound......so even little things that have no measurement changes can make serious improvements to sound (all based on subjective listening, of course). If you only believe in measurements than tweaking by ear seems unreal. For instance, I changed the output filter caps in the UCD Ncore NC400 module from polyester to modified Polyprops and also oriented the outside foil of the caps to ground. This would not be measurable....yet it was a significant sonic improvement according to all those who tried this mod (if you search, you can read peoples feedback on this forum). The values were the same so no "technical Class D design knowledge" was needed. In my experience, everything makes a difference....you can hear all kinds of things you cannot measure. This has been the classic objectivist versus subjectivist battle that has raged on for years. Some people only trust their measurement gear and others only trust their ears.....I trust both. However, the ear has the final say......it is, after all....something we hear.
Your amps have always gotten seriously great feedback. You are a really great designer. I hope you continue to make your amps better and better.