@silverback, @ChrisSU - thanks again for your inputs.
Can I ask with regard to the passive ATC 40s will my Uniti Atom or my NAP 250.2 be the weaker link i.e. replacing which one of these (NDX2/NSC222 for the Atom, NAP 300DR for the 250.2) is likely to have a more significant impact on the sound quality?
Funny how we hear things as actives were my preference but to your question I found the ATC’s reasonably fussy about what they being fed with so source first for me.
Gary
Btw the actives into a stream pre looks like a neat and dare I say it economical solution.
Gary
From what you have described, relating to the 100aslt, I wonder whether or not the source electronics or the system set-up left something to be desired.
Extrapolating (as I have not heard 100’s) from the sound I am now achieving from my 40’s, I would be surprised if they (the 100’s)had less impact than the passives.
Elsewhere, I have described my 40’s as neutral, but not anodyne. Perhaps they reveal their ATC studio heritage to a degree, but I would have thought that if the source was capable of supplying bass, the 100’s would have no difficulty in pumping that into the room.
I found that adding decent mains cables transformed my 40’s: bass deeper, better defined, with less room-induced bloom as a result.
I wish I had the space and the £££ to countenance the larger ATC’ s, but sadly, I don’t
I had a quick blast of the new streamer pre with the psu into active 40’s and indulged with sone ac/dc… polite it was not! Great head banging session!
My experience of having both passive and active forty’s, is that the forty actives will sound like the 100 actives imho 
I heard a Linn Klimax through both Active & Passive 40’s, the passives using 252/300 and the actives just the 252. The sound reproduction was very different. There were things I preferred about the passives (obviously down to the NAP300 sound I’m familiar with) and things I thought the actives did better. Both were bettered by the latest version of the Klimax through active 50’s though, and by a good margin, which I suppose should be the case.
I suppose what I’m trying to say is just because you heard the passive 40’s and liked them, you can’t assume you will therefore like the actives. And to then throw in the option of Sopra’s makes the whole thing way too complicated IMO.
I had the passive and active SCM40s on home demo at the same time. Passives driven by an SN2. You’ll find different opinions on the difference between the two versions, but from my perspective there was only a modest difference between them. Both had the same sound signature (excellent vocals with nicely balanced bass and treble - not showy like so many speakers seem to be), but the actives had a bit more drive and energy, presumably due to the extra watts.
I would have been happy with either set-up, but preferred the sound of the actives and also liked the fact that it removed the upgraditis that I knew I would have suffered if I had gone down the Naim amp route. Oh, and I also loved the lack of boxes. Two speakers and a combined pre/DAC. It’s the ultimate “anti-system” 
Which mains cables did you use. I’m currently using powerlines but never tried other options.
Gary
Regarding differences between the 40 and 100, the main difference is below 380Hz, with each model as you go up the range from the 40 having a different (bigger) bass driver and associated bigger box. The midrange of the 50 upwards are all identical, that in the 40 differing slightly in not being the high power ‘S’ version. Though not 100% certain, I believe the tweeters are all identical (other than where comparing an older model from one range with a newer of the other, however the different front baffle sizes and mid/treble unit positioning may affect the dispersion.
As for the active versions, aside from self-evidently not having a passive crossover between amp and driver voice coil and instead having direct drive and hence maximum control, the amps in the active versions will be intended to be neutral, and not modify the sound by stamping a sound signature. If someone likes their music presentation modified in some way by the amp, then the active versions might not sound as good compared to the passive driven by a preferred amp.
I’d say that the midrange on the 50s and up is quite a jump ahead of the 40s. I can’t seem to delete my earlier post, which I made having read IBs post incorrectly. Apologies
The only difference of which I’m aware between the S (used in 50 and upwards) and standard version (used in the 40) is the size of magnet, that in the S quite a bit larger than the already huge magnet of the standard, adding a couple of extra kg (even the standard version is heavy, mainly due to the magnet, weighing about 7kg per unit!). I’ve not read anything suggesting any difference in diaphragm assembly, suspension, or voice coil, even though it quotes a higher power handling capacity. The bigger magnet gives higher magnetic flux density in the voice coil gap, and higher sensitivity. I would guess that from the sound point of view it very likely makes for a better transient response, so maybe that is responsible for the difference, though I would expect the same sound character overall.
I got Titan Audio helios and 1 eros for the Supercap, plus a Titan Nyx mains block
Total cost about 875 buying “offers”. Biggestvimpact on the speakers. They trabsformed the sound in my small room.
It wasn’t an Eros, ut was a Helios Signature. I am typing this before 5:30am, so am allowed to not know what I bought 
Thanks BigAI, I”m currently using Naim powerlines and a music works G3 as that’s what dealer was using when I demoed.
Thanks for info re your set up.
Regards
Garys
It must depend also of which external amp you use in the passive configuration. For example ATC active can sound better vs ATC passive with Nap 250 dr but the same passive ATC may sound much better with Nap 500 dr than the active ones.
Thank you all for your inputs, much appreciated.
Any thoughts on my question on which is the weaker link in my current setup (Uniti Atom or NAP 250.2) if I do go the passive speaker route, either with the passive 40s or the Sopra 2s?
Am asking since I will only be able to get one of these now and will have to wait a year or two before getting the other.
I’ve auditioned ATC40 several times with naim and although obviously very refined and correct I found I needed just a bit more emotional and vibrant speaker. (Perhaps after many years of being brainwashed from the lively Naim Ariva.)
Ended up with a trade-in Graham LS5/9f a bit by random. Already at initial listening at the dealers they were everything I was looking for. Rolls off at 40hz too like the ATC and I was a bit concerned about that since my old Naims went down to 30hz. (But Naim a bit boomy, atleast in my room, think I have a big room-mode between 30-40hz)
Taking the Grahams home only accentuated the strengths I heard at the dealers and really it comes down to how they sound in your room. For me I got so much better bass now and lively rich presentation with more refinement all across the board. So Graham floorstanders (LS5/9f, LS6f) worth looking in to imho. Otherwise, try to take the ATC home for a tryout 
Indeed you’re right it may - and it would be interesting to learn of such comparisons, ideally by multiple people.
The SCM40s are infinitive baffle speakers (sealed box) and do not use a ported enclosure like the rest of the range upwards of the 40s.
I suspect that this is in part responsible for the 40’s curtailed bass response and ‘the punchier sound’