Just to add to this legacy thread. The RS4 were my first set of speakers, purchased in August 1978, after comparative demos agains the likes of Bose (301s!), Swallow, KEFs etc. They offered very pleasant tonal balance with subjectively a slightly recessed midrange and superlative imaging. I started off driving them with just the original A&R A60 integrated amp and ultimately ended up with a Naim 42/Hicap preamp and an Audio Research D70mk2 power amp (which by itself cost 10x what the Tangents cost). With the Audio Research they had a gripping and totally immersive sound that was near impossible to beat. I tried to upgrade them and did home demos of Gale 401, Magneplanar SMG, Linn Kans and Saras and possibly a few others too, but none of them came even close to what the RS4s were doing.
For a while I used them as a guitar speaker, plugging the guitar in to a cassette deck with the record gain set to the max turning it into a clipping fuzzbox. These waveforms and the volumes I put through them did causes some crossover thermal damage...the foam next to the power resistors was melted and scorched, but they never stopped working.
I also found the RS4s to improve enormously when the 6 inch high castor wheeled stands were replaced by some heavy duty spiked HB1 stands at 18 inches. I also rewired the innards with Naim NACA 4 speaker wire which was a modest improvement.
I sadly sold them to close friend in 1985 as I was moving continents. Had I stayed there I may well have been using them to this day. I can only imagine what they would sound like if the crossover was assembled with 2012 audio grade components.