With 'stats, everything matters...
It should be a blast with plenty of cool electrostatic stuff. I'm planning a high-end transformer box and then there is the T2 DIY version, perhaps a DIY Egmont amp plus what ever Kevin brings.
The box is a bit anti-climatic when compared to the HE90 unit but it does its job...
It was probably a mix up at some point, at the original Stax dealer or even Stax in Japan. I've never seen a 520 or higher S/N so they are certainly some of the last ones made.