My amp beats AG's amp!
Well, you're wrong. I know I've said that a lot here, but this time I can prove it.
I went ahead and simulated your circuit in LTspice, as you gave it in
post #16 here (.asc file attached below: notice the "AG" suffix):
**broken link removed**
I checked it very carefully against your posted picture, and I don't think I made any mistakes. (If I did, please point them out.)
When I run it, I get a distortion figure (using LTspice's
.four function) of
3.45%. Not too bad.
My circuit, however (minimally altered from the original one I posted and also attached below) gives a THD of
2.16%.
Therefore, at least by the measure of THD, my amp is better than your amp. In other words, your so-called "improvements" didn't improve anything.
If you don't believe me, you can run it for yourself.
Next?