David, I have not noticed any negative aspects of dCS performance that could be laid at the door of them having inadequate power supplies neither,I expect, have you. So I think this is basically a rhetorical question.
Of course big power supplies that need a separate box may indeed be appropriate. Perhaps even more appropriate in an analogue amplification scenario.
The original Naim pre amp had no power supply of its own and was powered from the power amplifier. The first separate power supply, SNAPS came later. At the time the Naim 12S ( or K) plus the 160 or 250 were amongst the most costly solid state amps made in the UK. Julian Vereker was a canny entrepreneur and I would not be surprised if powering the preamp from the power amp was not a way of attracting customers by keeping the cost of membership of the Naim club lower than would have otherwise been the case. Of course once SNAPS came out and was successful this provided an upgrade path. JV and Ivor Tiefenbrun, in their mutual axis of the time, were keen of getting customers back in the shop for an upgrade on a regular basis. Selectable power supplies is a great way of creating repeat business. Cynical? Not really, a company has to make a profit to survive.
Of course not all two box components divide the responsibilities between active circuitry and PS. Some have a “clean box” , “dirty box” configuration.
I am sure that dCS ,in their 32 odd years, will have considered these approaches but, at the time, rejected them for various reasons just as I expect they have considered and rejected adding room correction dsp or a tube output stage and many other options. Still, who knows what may come along in the future?