I've known Alan since 1988, a year or so after he took on the brand and have had *plenty* of dealings, edited posts and all-but-banning over on the HUG before I got my stuff together and calmed down enough
He obviously has his brand first and foremost and that dictates how seriuously he takes his largely non-we customer base and the simplistic 'education' which is quietly being slipped into HUG topics, but the current XD models I've seen tested measure very well in conventional terms apart from possibly dispersion which is still predictable (and he LISTENS for hours and hours before signing the designs off and as my [Non-ATC] flat earth indoctrination of the 80's and 90's suggested, a dB or so on tweeter level may not show much in measurement, but it can be heard and sometimes not for the better!). Prices won't be low, but he now claims to have a Klippel (Klippel to what level I'm not sure), he has at least two or three other graduate at least and properly qualified engineers in the design team and he claims they're well advanced on active prototypes with DSP as well as further research on the cone material that does work very well if natural sounding speech and acoustic instruments are important. The main thing is, knowing the man, is that any new model will have been VERY thoroughly gone over before being released to market. Harbeth is definitely not just a one-man-band any more and is rather more a family concern with good assets and not such a small UK business now. I appreciate the above may not be of interest to the ASR Klippel-Chasers, but it's a worthy brand and each new generation has been a genuine evolution over past models (why with sorted hearing I now hear how basically good my 2007 issue 5's are).
Just to say the radial coned drivers don't go off or harden up as many Spendor drivers do (why do you need a sub in your setup - have your bass drivers 'gorn orf' as the S100 has a rich-weighty balance from memory?) Don't ignore the current 7-XD as its a way better speaker in tonal balance than its ES3 predecessor (all the former 'grand-ripeness of tone' has gone) yet still has a little bit of bass weight and now sounds genuinely like a smaller 5+-XD. The old ferro-fluid Scan tweeters in the S100's can lose output a little as well I believe as the fluid dries out so making for a less lively sound.
Apologies all - I'm no shill for Harbeth, (or ATC for that matter) but I do know these brands better than perhaps many viewers on here, especially Harbeth as I get to hear the new models regularly. You have S100's which I also know a bit first hand, so merely trying to suggest modern replacements which will equal or surpass the better bits of the S100 but in a smaller package. I could never ever spout forth about Genelec and Neumann as I simply don't know them and the KEF guess is based on experiences with passive speakers with a definite flat to rising lower kHz region compared to models with more 'subtle' lower-hf balances.