Hi Breeceboy, thanks for your offer to seek this out: I gather back issues of Listener have never made it onto the internet.
I am afraid I cannot direct you to a particular issue: there were S100 reviews published elsewhere from May 1989 (Martin Colloms). The S100 became the SP100 around 1994, I believe.
I have the impression the review may be 1992 or 1993 (at the latest), since Art Dudley talks about having used the S100 as his reference 'for 8 years' in a review he wrote in 2003, by which time he had clearly moved into low output valve amps. & alternative speaker types in his own system.
Sorry to be so vague: I am very grateful for your help with this.