Advice from anyone with Tangent RS4 speakers?

Well, I woud not be surprised if I am the only one that knows anything about these. They were made in England circa 79-81. They used drivers by Audax of France. An 8" bextrene woofer mid and the ubiquitous 1" soft dome tweeter that almost everybody was using at this time. The Bextrene driver was a nice sounding unit but was very inefficient at around 84 db and also did not handle much power, around 40 watts rms was it. So the RS4 is a very British sounding speaker, if memory serves, warm and full in the bottom and slightly rolled on top. Because it is so inefficient and very limited as to how loud it can play it is definitely not for headbangers. I would say that you need an amp with a little grunt to drive these. The NAD would probably do it. I would go with an amp that has a neutral balance rather than overtly warm simply because the RS4's are already on the warm side.

Good. That's just the sort of advice I was looking for. Thanks. I'll audition the NAD.

I guess you already bought your amp, but I can't resist sharing a few comments on these lovely old speakers.
I am listening to my RS4s as I type this. Bought them in December '78 and have never found a reason to get rid of them. No - they're not the ultimate audiophile loudspeaker, but incredibly difficult to tire of. Very warm, comforting, BBC sound. Not good for high levels (the crossovers tend to melt, leading to 1/2 hour's soldering to put everything back into the PCB) and not efficient - I have had best results driving them with something around 80-100W RMS. Currently they are playing MP3s from my PC via a 100WPC Crimson Elektrik (circa 1980) power amp. A couple of decent stands (shot-filled is good) to lift them about 18" off the floor tidies up the bottom end. Just don't drive them with anything that's woolly in the bottom end - my worst ever mistake was a Velleman valve amp - sweet at the top, but utterly suffocating in the bass. Get the amplification right and enjoy!