"I’m not personally familiar with the Hashimoto but it has the reputation for being a very good output transformer."
I own Hashimoto OPTs and interstage transformers. The OPTs are double C-core and are designed by former Sansui transformer engineer with over 50+ years of experience. Hashimoto doesn't believe in using silver or nickel in their transformers as they feel these metals do not sound natural. Only copper and Japanese steel are used. Hashimoto has excellent reputation and is on par with the best Japanese transformer manufacturers.