Hi Matt! Thanks for asking, and good questions.
B&Ws: DM330s handed down from my father; then CDM1SEs I bought myself, followed by CDM1NTs I found used for a great price, and finally original-gen 705s, used for an even better deal. DM330 to CDM1SE was biggest single step up, but 705s were easily the best of the bunch (cleaner mids, much better tweeter, better imaging), and I loved them. Their limitations were obvious, but they have decent directivity so it was easy to EQ down their treble boost, and their room reinforced bass was good enough for enjoyable listening. They were a bit flat-sounding and underwhelming with some material, but never sounded bad or "off" with anything, so really easy to live with once I got them placed and EQ'd to my liking.
Genelecs: 8351s, best speakers I've ever had (and they damn well should be given the price - yikes). Frequency response: more linear than the 705s, and their bass F3 is an octave lower. More energy, impact, and control around the 50Hz kick drum area, and no excess energy around the 80-150Hz area. (Probably why some folks say Genelecs sound lean/bright - they have no mid-bass hump.) Imaging: strongest suit of the 705s, especially the phantom center. But the Genelecs clearly exceed them even there - super-strong phantom center, and at all image locations the Genelecs provide enhanced perception of air/ambience if it's in the recording, or more in-your-face flatness or presence if that's what's in the recording. Soundstage: more or less same width as the 705s, but the Genelecs throw out a modestly taller image, even though I'm pretty sure their concentric drivers are physically lower than the 705s' tweeters. Depth is superior on the Genelecs, mostly because the superior imaging cues enhance the illusion. Distortion: Genelecs very obviously cleaner - that air/presence at different image locations must be at least in part from lower distortion, as is the tighter, more linear-sounding bass. Plus physics, measurements, and common sense tell us there's no way a 20 year-old, 2-way design with a single 6.5" midwoofer built to a $1500 price point is going to compete with the 8351s on distortion performance, especially below a few hundred Hz.
Between the 705s and the 8351s, I had my father's Infinity Kappa 9s as my main speakers for a couple of months. So...
Genelecs vs Kappa 9s: Much more apples and oranges. Frequency response: Kappas have more potential (2x12" woofers per speaker vs two 4x8.5" for each Genelec), but in-room measurements show the 8351s getting to within about 5Hz of the Kappas. Perceptually, bass is different in a way I find hard to describe, but functionally the same/as good at my 75-85dB @3M (aka 85-95dB @1M) typical listening levels. Midrange - both are excellent but Genelecs sound cleaner and smoother. Treble - the Kappas are excellent in some respects but suffer from sibilance, and I've struggled mightily to EQ that down while preserving satisfying perception of treble detail/energy/air. So the Genelecs stomp all over the Kappas in this area, as the Genelecs are smooth and detailed throughout. Imaging: Kappas are less precise than the Genelecs (and that's with Dirac correcting speaker gain and impulse response for the Kappas), but I would not describe the Kappas as deficient, and one can clearly identify the locations of everything with the Kappas. Soundstage: Same width for both, but Kappas win on height, which makes sense since at least 3 of their drivers, covering upper-mid and treble frequencies, are positioned up to a foot higher than the Genelecs' drivers. Depth is similar for both. Distortion: I have less confidence in my subjective impressions on this, but that said the Genelecs just sound cleaner and smoother overall, especially above 1kHz. Speaking of which, the Genelecs sound more cohesive: 4x concentric drivers in a 3-way design seem to work better than 7x drivers arrayed as far as 3 feet apart from each other, even at 3M listening distance.
Overall I'd describe the Kappas as dramatic and the Genelecs as accurate. If you give me uniformly well-recorded music that specifically has no vocal sibilance, no prominent brass, and no prominent electric guitar harmonics, and ask me to listen for 15-20 minutes at fairly high volume - like for example putting on the first couple of tracks from Dark Side of the Moon and just cranking it - I'll probably pick the Kappas.
But if you give me my full music library, with lots of different genres and lots of well-recorded but sonically varying material, and you ask me to listen for 30, 60, or 120 minutes at a time, at a variety of of low, medium and high volume levels, day in and day out, then I'm picking the Genelecs, no contest.
Finally, I should note that I prefer slightly narrower dispersion, and I prefer precision over envelopment to the extent that I have to choose. I love the drama of wide dispersion and a huge image, but for me it's like dessert: I always think about it and always look forward to it, but I can only actually enjoy it in limited portions, and after that the same qualities that I loved become excessive and unappealing to me.
