Clarification: I should have stated: " Stan Warren's output stage offers unparralled sonic and electrical performance, as compared to ANY "drop in" replacement, that is available to the other modifiers. This makes his gain stage very esoteric indeed."
As a former Sales Enginner, who has represented a high performance IC's manufacturer, with 1200 different types of IC's, this is my qualified opinion.
Stan came up with his circuit design based on sonic comparisons of various circuit implementations, and compared them to these "drop in" replacement devices.
Stan has not always implemented his proprietary circuitry.
In his modifing past, he also used and implemented the best of the best "drop in" gain stages. This qualifies him to understand all of the variations, and their inherent sonic performance charactaristics, along with their limitations.
I have personaly told Stan to charge MORE for his services. I feel that many people overlook him, because they perceive him as a budget guy's modifier. In reality, he is nothing less than world class.