The 323 had a p-channel jfet as the input, +/-350v power supplies, 2sa1968 as the current source for the drivers etc.
The 353 is a srm717 with all of the extra transistors removed. Very similar to kgss. D50 is identical to 353 running at slightly lower power and lower voltage. Current source is resistors on both.
T8000 also uses resistors for the current source.
seems that stax has run out of 2sa1968.
d10 uses apex opamps with a power supply of +/-175, not great for large voltage swings.
stax may be forced into using parts in the future that it does not want to use for some reason.