I seem to recall that (Sony) Superscope bought Marantz in the late 70's-early 80's. Although there are a lot of things I don't remember about back then, like 1971, 1972, etc.
Sigh.
Something like this gets repeated over and over again.
Saul Marantz sold the company to Superscope in 1964. All the classic solid state Marantz gear of the 70's came out under Superscope's ownership. Superscope's claim to fame was that, at the time, they imported all Sony's tape recorders. This is the closest corporate tie that has ever existed between Marantz and Sony.
In any case, Superscope began producing Marantz products in Japan in partnership with Stantard Radio Corp. (SRC) in 1966. Eventually, Superscope would own a 50% stake in SRC. SRC changed its name to Marantz Japan Inc. in 1975 and by shortly afterwards was manufacturing all Marantz gear. It was around this time that the Superscope-branded components mentioned in the OP were produced.
In 1980, Superscope sold its interest in Marantz Japan Inc. to Phillips, only retaining rights to the name in North America. Phillips, at the time, was jointly developing the compact disc with Sony, but was a separate company. In the 80's, under Phillips, there was certainly some fine gear produced. Overall though, the quality declined. The schizophrenic appearance of the brand in North America (Superscope silkscreened "Marantz" on some pretty horrid equipment) contributed to the tarnishing of the nameplate in the public perception.
In 1992, things started to turn around. Phillips acquired the North American rights to the brand and set about polishing it. In 2001, Marantz Japan Inc. bought out Phillips' share in the company, consolidating ownership of the brand in one corporate entity for the first time in sixteen years. The following year, Marantz Japan Inc. and Denon were acquired by a Japanese-controlled consortium and D&M Holdings was formed. They seem to be doing a fine job managing both brands and have been rapidly acquiring venerable hi-fi companies, for the most part letting each division work independantly.
Is everybody clear? Marantz has never been owned by Sony. Ever.
http://en.wikipedia.org/wiki/Marantz
EDIT: Wow! For the authoritative tone I took, I sure got a lot wrong. Expect some expansion and correction soon.