^ I'm certain that JBLesque tweeter diffuser is another "field installed upgrade". It would make installation of the grill cloth impossible, just for one thing. It's also the first time I've seen an undersized square diffuser installed over a round tweeter.
These (S-50) are probably mid to late 1980's models. I haven't done a deep dig on them yet. But they resemble the sort of speaker systems Sansui was making from about 84-89. Quite a few models were made with the S prefix (the SP and others previously used having been dropped by that time). Some were better than others, I've seen some ultra cheap rack system models of that era that were made in the US, because it was cheaper to do that, then to import speakers of Japanese manufacture for anything but high end models.
The last really properly good speakers Sansui offered in that time frame were the PM-C and XL series. It wasn't until about the mid 90's or so that they resurrected the SP line with some very nice (and high dollar) bookshelf models. The SP-100i was one of these offerings, and have been discussed here on AK before.
All that said, I'd be curious about these myself, as they are not at all commonly seen, and were probably sold seperately, rather than as bundled rack system speakers. The cone midrange doesn't impress me much, but I've been surprised before by what looked to be basic, inexpensive drivers. It doesn't have to be exotic to sound good, though that can help. I'd be most interested in the quality of the cabinet construction. That fell off a lot in the 80's, and not just for Sansui.