Well ok, depends which R652 we are talking about, they changed around 1986-87.
First I believe they changed the bass/mid driver because the dustcaps (which protect the voicecoil maget gap) kept falling off. Nope they don't make 'em like they used to.
Then later, or maybe at the same time they changed to the metal dome HF driver.
BTW the cabinet was the biggest problem, stiffening braces for the side panels (even very simple) is well worth the effort.
I'm familiar with Robin Marshall, I used Epos ES14 in the 80s in my second system. The bass was rather 'fruity', but there again the amplifiers he was using as a reference at this time were, well I thought a strange choice as it could not resolve the bass that well. It was a nice sounding amplifier though, in its time (1975).
Incidentally the ES14 bass/mid driver did not require any crossover, it rolled off naturally.
In comparison the slightly later, but more expensive ProAc Response 2 did require a crossover network. The results were far superior though. As an engineer who admires elegant, I mean simpler, or dare I say zen like solutions, I totally get the idea that one might expect better results but it doesn't always work that way.
As to new MA speakers you should check ot these reviews of the Silver 500 7G, they're really good!
www.stereophile.com
Hot off the production line, this flagship of MA's 7th-gen Silver range marks a significant uplift in performance By now, there's surely not an audiophile alive who doesn't know that Monitor Audio's Platinum loudspeaker series is its pinnacle, and that as you move down through Gold, Silver and...
www.hifinews.com