Room Correction

I think the apprehension about digital room correction is misguided. Analogue is by no means superior (that is an audiophile myth).
Room acoustics should be divided into two areas: above and below the so called Schroeder frequency, in your case probably about 130 Hz. Above that, all you can realisticaly do is apply a bit of damping with rugs, bookcases etc. Below the Schroeder frequency the resonance peaks (and dips) are so far apart and so large that they can be distinguished quite easily, and greatly disturb the sound, with boomy bass and slow decay (hence the term slow, which in reality refers to the room rather than the speakers). If you look at the in-room frequency response of speakers the deviations from a flat response are truly horrendous (easily +/- 10 dB, compared to +/- 0.2 dB for good electronics), and completely mask any imperfections earlier in the chain. So something has to be done.
Full range main speakers have the disadvantage that they have to be located for best midrange response and that is not necessarily best for bass. So many people prefer separate subwoofers that are designed for deep bass, and can be located for best bass response. However, just one sub will still give huge peaks and dips. Hence the method to smoothen this with multiple smaller subs. See here for a clear introduction and further links: http://www.acousticfrontiers.com/20101029using-multiple-subwoofers-to-improve-bass-the-welti-devanti...
On top of this, equalization is still very useful, and more succesful with multiple subs than with one, because the peaks are lower, and because the equalization will work over a larger listening area. With one sub, the response will only be correct in one listening position.
There are various ways to equalize the response. The easiest is to use a DSpeaker Antimode 8033 for the subwoofers. It is an automatic system that analyses the in-room response of your subs, and then designs and applies a correction curve. see here: http://www.theabsolutesound.com/articles/dspeaker-anti-mode-8033-dsp-subwoofer-equalizer-tas-204/ I use one with great success.
The alternative is to do all the hard work youself, with the REW software and a calibrated microphone. Correction can then be achieved with a miniDSP unit. This is a bit cheaper, but I would not bother (REW is quite hard to use).
DSpeaker is about to introduce a complete preamplifier/DAC/room eq system, the X4, but that is expensive and may not be necessary.
Finally, and perhaps not of much use to you, but dipole speakers like my Quad electrostats suffer far less from room modes, and hence have an exceptionally clean sound. However, they are huge, and need space (at least 2-3 feet for the smaller 2815 model, and more for the bigger 2915) behind them (but not on the side). If you can find room for them, they are gloriously absent: you hear music rather than speakers. They also have dynamic limitations, but should be fine in a room like yours.

Well, setting up your speakers properly is certainly a lot less hassle than forever worrying about cables. It also makes a far bigger difference. As the guide Michelin would say: vaut le voyage.

It is a myth. Just read up on the Nyquist Shannon theorem. If you can refute this, you are in line for a Nobel prize.

I agree that good acoustics are important. However, below the Schroeder frequency this is basically a matter of the size/dimensions of the room. The bigger the room the lower the Schroeder frequency, and the more the inevitable room modes can be kept away from the main listening frequencies. Unlike above the Schroeder frequency, at these low frequencies normal damping material will not help - you need large and ugly bass traps.

That is how I do it is as well. Not because I believe the digitization degrades the sound, but because room equalization above the Schroeder frequency (in my room about 90 Hz) is not feasible. Of course, just equalizing the subs leaves the bottom end of the main speakers below the Schroeder frequency unequalized. This is where a large room is beneficial, and/or some equalization of the main speakers´ bottom end. But equalizing, say, 150 Hz produces a very localized benefit that may not be worth the trouble. Fortunately my Quad stats are dipoles and hence do excite far fewer room modes.

Absolutely. I looked into dipole subs, but there was nothing on the market here in Europe. Also, the designs that I saw were huge: how could I reasonably persuade my loving wife who already puts up with the Quad electrostats?

Thanks, that is interesting, and Kenny’s subs do indeed look good. However, they are still too large in my situation. My B&W PV1d sits discreetly tucked right into the corner behind the Quads, and thus virtually invisible. That position (advised by the DSpeaker engineers) also gives some nice corner reinforcement that is then equalized by the Antimode. After recently reading a lot more about subs, next on the shopping list is now a second PV1d for the corner behind the other Quad, for more power and a smoother response.