I'm not an expert but I have 2 alpha 907s, a D-907F and an AU-XII and as I've mentioned the alpha 907s sound significantly more powerful than the D-907F and even the AU-XII. Why, I don't know except the original alpha 907 weighs 30kgs. (the imos Ltd weighs 32kgs.) and uses toroid (the D-907s weigh from 20 to 26 kgs. mostly with traditional EI transformers) although the caps rating in alpha is less than 80,000uF which one finds in the D-907s. In my collection of amps, only the alpha 907 could properly drive the 15-inch woofer in the JBL 4430, whose recommended power to sound its best is 300wpc RMS @ 8 ohms. The 4430, I was told a long time ago, was the waterloo for many tube users since its woofer is power hungry. BTW, alpha 907's sound reminds me of vintage Krell and Stasis heavyweights -- my dream amps -- I auditioned in the US back in mid-90s.
Going to another topic, Southpeak has proven that a patient hifi enthusiast could find gold in Metro Manila's used market and at reasonable price. Previously, there was this belief that the heaviest upscale vintage Jap equipment only lands in Davao. I still remember when he asked me about the LoD HMA-9500 early this year and I envied him for his find since it was a sought after model even in Japan. Despite its comparatively modest power rating, it was I think Hitachi's TOTL power amp during its time with premium-grade parts and timeless design/appearance. Anyway, Ben also owns a Sansui AU-111 valve amp made in the '60s, now a collectors' item, and many other high-end equipment -- better in quality and higher in resale value than those I own.
Here's a trivia. Ever wondered why Hitachi used LoD for its domestic brand? Hitachi, a certified sogo-sosha (giant Jap trading firm) wanted a unique name for its audio line considering it has so many products including personal care and small home appliances. The race was for the "lowest distortion" amp that could be developed. (Remember, it was shifting from the tube amp, which traditionally has high measured distortion) Hitachi's low-distortion objective became the brand: Low D; eventually becoming "LoD."