I haven't owned the 34/405 (I had the 33/303 pair for a couple of years with some circa 1980 - pre body stocking - Mordaunt Short Festivals) but I have heard the FM4/44/405 with Quad ESL63's quite a lot in the past.
Although it was always an amazing sound, especially with radio*, I cannot comment on their use with conventional moving coil loudspeakers.
* The FM4/44/405/ESL63 together constituted the best 'radio' I have ever heard. Particularly with BBC. They were made for each other
(Sadly, it was not my system though.)