Ah, one of those. Sansui first used the Classique branding on reissues of certain models (often with cosmetic tweaks) that were sold as part of a bundle system (receiver, turntable, two speakers or similar) so essentially a precursor of the rack system marketing approach that hit full bore about 1981-82.
The Classique 550 was thus a quick and easy way to squeeze a few more dollars (Yen?) out of an existing model nearing the end of it's run and which already had it's sunk costs long since covered from previous sales. There is a good chance it was originally bundled with an inexpensove semi auto turntable and a couple of very average mass market speakers when sold new. Also, probably was sold at a department store or a deep discount dealer ike Crazy Eddie's (wasn't that the name fo the joint?).
These combo systems were a marketing gimmick probably done at the behest of certain mass retailers so they could sell a complete functional system at one price, and avoid comp shopping (and price matching) at the same time.
This is still common practice today with big retailers like Best Buy or Walmart who have enough pull to get their own versions of a product like a TV or computer that often are nothing more than a model number change of an existing identical product. Presto, no price matching or comp shopping possible because "oh, it's a different model". Heh, yeah. What you did there; I saw it. So slick you almost had me fooled.
The first few applications of the Classique sub-brand were in the lateish 70's. It really got heavy use though starting in about 1981 with several of the Super-compo series models being offered concurrently under two model numbers, one conventional like the T-7 tuner or the A-9 integrated amp as a couple of examples, and alternate versions that were virtually unchanged save the model number and having the Classique designation applied.
This practice continued into at least 1985-86 from what I can surmise from ads and marketing material of the era. Later iterations from 1983-84 onward may have actually had cost reductions made to the Classique badged models by way of omitting a feature or two as a means of further justifying the split-identity product lines and further enhance the profitability of the decontented versions.
What is the serial number on that Classique 550? I'm curious now to see if it falls within the regular production timeframe of the 6060/690 that obviously spawned it, or if it was made a bit later to milk the already extant tooling and production capabilities to get another few months of additional profits from the 6060's "carcass" after it had been discontinued. If there is no overlap in production dates, then I suspect the latter to be the case. Obviously it will take more than one data point to establish that.