FWIW the schematic is here
http://bee.mif.pg.gda.pl/ciasteczkow...A500%20amp.pdf
There are a number of merits to the overall design, not least of which is that all the other transistors are current parts.
The output devices are complementary Darlingtons with built in temperature compensation, so the design does not need the normal Vbe multiplier and removes thermal tracking issues. Sanken parts, alas discontinued.
The design seem to come from about 1999/2000.
Craig