There is a GAS Son of Ampzilla for sale on US Audiomart. I have been involved in high end audio for over 40 years and started off with a Son of Ampzilla and Maggie SMGa speakers. While I have had some 30-odd amps through the years, I held onto the Son. It has an entertainment factor other amps just seemed to miss. I have used it with other Maggies from SMGa's, MMG's, 1.4's, 1.6's, and 3.6's. It always handled the Maggies very well.
I had a reference mod performed on it by Mike Bettinger with GAS Audio, formerly GASWorks. I am currently using it on Wilson Audio SabrinaX's and just love it. I have auditioned it against a Gryphon Diablo 120. While the Diablo did have aspects that were better, it wasn't enough at all for me to walk away from the Son. The Son held it's own in that one too and proved again it is a great value.
The nice thing about the Son for sale on US Audiomart is it is in great condition and has a basic mod performed by GASWorks to boot. I should think it would check off all the boxes in your search criteria, especially for the asking price of $750. I do not know the seller, and that being the case, do not represent him.
Good luck.