@rfc --
Irrespective of the difference in volume levels (and room/gear) between the two setups, i.e.: the Spendor vs. ATC system, what was your main takeaway in terms of the core traits you heard from them? While not an optimal context of comparison it’d still give you an overall bearing on the fundamental sonic differences. The ATC speakers I’ve heard, all of them active iterations (that is, incl. one pair of passively driven ATC SCM100’s, fed by a Crown Studio Ref. II), to my ears are particularly well sounding at "normal" listening levels - say, 75-85dB’s and above. Maybe that’s indicative of both the way they’re balanced and how relatively unflappable they are at higher SPL’s due to their great, low distortion drivers and active config. Which is also saying that to some degree at least their pedigree at "normal" to higher levels isn’t due to them being lesser performers per se at lower levels, but because they’re somewhat more effortless at higher listening levels than most hifi speakers. For sure the brilliant 3" midrange dome of the active ATC SCM50’s will wring out more information, clarity, intricacies, composure and dynamics than the Spendor’s, by a mile - while being an extremely coherent sounding speaker package top to bottom - but that’s not necessarily to say you will like them more overall.
The advice given by Erik on a separate preamp vs. DAC-direct isn’t irrelevant. Personally I have a dedicated studio segment DAC/preamp (with a great analogue output stage, PSU and volume control) coupled directly to my power amps, i.e.: via a digital crossover, and the range of separate preamps I've tried haven't yielded a more "meat on the bones" imprinting nor other that would make them the more desirable option. It certainly depends.