Cool! I never would have suspected Sony but.....
I'm willing to bet that these are actually built-to-contract under the Superscope distributor's rights to use the Sony name. I note from the manual's pics that it was called, Sony Corp. of America.
Later models of Sony speakers were made in Japan once Sony's agreements with Superscope were concluded. This was about, IIRC, that the first Trinitron TVs hit the market, too, which really did put the Sony brand out in front of most consumers. Once that happened, it was a _lot_ easier to sell Sony receivers over Pioneer and Marantz.
Cheers,
David