Four different amplifiers, class AAA, class A, class A/B have been used successfully in my systems with Schroeder Method. Avoiding class D as per warnings about potential amp instability with Schroeder Method. However, it would be interesting to test it with a cheap class D, perhaps a $100 amp if one can be found.
The initial concern about suitability of the Method for use between pre/amp has been at least partially addressed. However, until such time as the Schroeder Method is fully vetted and the parameters of use fleshed out this is a do at your own risk activity. See manufacturers if you have concerns about suitability for your gear.