And so I would recommend `activeness' whole-heartedly. But the inevitable question which gets asked (does get asked of me quite often in fact) is, might it be worth going active with a pair of amps such as 140s rather than going for a single passively used 250?
And I suspect there is no set answer, as it will inevitably depend on what speakers you are using among other things. However I have convinced myself in one specific case. I have compared Linn Kans (which I feel have a pretty nasty crossover in them) being driven actively by my four `135' monoblocks, against using just a pair of 140s. Not surprisingly the monoblocks sound a hell of a lot better! But even with the 140s, that essential active speed and musicalness was there. It was undoubtedly streets ahead of the rather sluggish passive alternative in terms of timing, musicalness and openess I feel. Driving the speakers passively with large amps certainly gives more bass compared to the active operation with the smaller amps but I think slightly less bass is a reasonable sacrifice to get that active feel.
By the way, note that when Naim use their stereo amps in active systems (the 250 basically) it is connected up such that you have one amp per speaker, rather than one amp for treble and one amp for bass. In other words one channel of an amp does treble, and the other channel of the amp does the bass. If you are wiring stuff up yourself, you might like to try both methods just in case there are specific instances where keeping the treble and bass in separate amps might work better (for example you undoubtedly get somewhat smoother treble with a separate amp on the treble, but might compromise the bass control especially if you like things loud). On the whole though, my chosen path would be a pair of 250s, with one stereo amp per speaker. You might also consider a system which has a more meaty amp doing both bass channels (say a 180 or 250) and a smaller amp doing the treble (a 140 perhaps). I know one person who operates that way with a bi-amped system (rather than active).
Recent footnote (Oct99):
I have recently moved to B+W Nautilus 802 loudspeakers, driving them passively with my 4 monoblocks. After listening to a lot of really high quality speakers I have convinced my self that passive crossovers need not be nasty if well designed. If the speaker is good enough (and I admit that tends to mean damned expensive) the passive crossover does not draw attention to itself, nor appear to muck up the music or timing. Of course ultimately active will always be better (eg, note that the B+W original huge curly Nautilus design is a fully active 4 way design) but it is encouraging that at least some loudspeakers I have heard do seem to be able to sound `active' even when being run passive (and I've just bought one of them!). Naim and Linn speakers however aren't in this category however, and perhaps that is deliberate considering how much revenue they must make from an active upgrade path. So in summary, even though I am running passive now (essentially based on the philosophy that a very good passive speaker is better than a not so good active one), I am still a big fan of active operation. Who knows, perhaps one day I will take the 802s active....!