I'm getting started with an old STAX classic, the SRM-1/Mk2 PP that Spritzer sold from his collection just a while back. And having compared the SRM-1 with the SRM-007tii (stock) at an audio shop, i didn't feel i was missing too much but adopting the older STAX amp.
Sorry to say i've no other experience with those amps you listed (SRM-323, SRM-006t or the works).