Always interesting how threads develop among dedicated listeners...
I'm happy to see TAI friends and Swan D2.1se owners present and accounted for!
At any rate, perhaps readers will allow me to answer a few questions pertinent to this design, and if they don't mind, maybe I can add some personal thoughts and insights about it as well.
With a year's experience behind this model, I think it's safe to now suggest that the D2.1se appears to offer the audiophile the somewhat more traditional 2-channel experience, one where a single pair of 6.5"-based high-power stand monitor 2-ways can, when driven with commensurately excellent electronics and sources, develop a bona fide, powerful soundstage, complete with height, width, depth, and weight, and including a sense of each instrument (from within great recordings) occupying it's own "envelope" of air or space.
Whether or not this is customary for designs in the broad market built specifically for home theater and/or driven with budget HT electronics, or even designs built to a specific objective measurement goal, is frankly unknown to me, but in my view on the D2.1se it speaks to the refined stereo experience -- at TAI, this is the effect we were striving for in the original spec. We freely admit to seeking the listener's visceral, emotional reaction -- I'm not sure who said it, but IIRC the D2.1se once struck him as "the 30 year-old Scotch" of the genre. Hopefully, this design is about musical pleasure (at least as best we can deliver it at the given value level -- the retail shops were only occasionally populated with comparable designs, IMHO, costing $1000/pr back in the late Eighties...and in '80's dollars.)
And yes, D2.1se's naturally then sound something like what you drive them with -- that being among their mandates -- probably questioning the choice of a sub-$399 receiver (with a few exceptions). I recommend that any 85dB design (measured anechoically and therefore w/o room gain) be driven with a high-current design, or an amplifier that doubles or nearly doubles its power into four ohms. The D2.1se is not a particularly reactive design, but at 85dB or thereabouts, it naturally likes a bit of "drive" behind it, especially when you want to explore it's ample power rating, one made possible by the oversized voice coils and ventilated motors. The Emotiva's mentioned in this thread certainly qualify. D2.1se's can go thereby "big" when pressed.
In sum, the D2.1se is voiced not only to be measurably flat within typical spec, but to have the voicing "trim" that grants it, users report, that dimensional picture on the performance. In that regard I personally find them to more resemble speakers from back when for-music designs were first measured and then rigorously voiced by ear. And as Ingbruno notes above, "these speakers will let you know when you change something." Part of the D2.1se's intended design goal includes lowered motor distortion and damped moving assemblies, the resultant "blackness between the notes" of which should typify the design school. Changing something else upstream likely changes them -- not always dramatically, but still as it should be.
It's a different effect, to be sure, and one that not all may find immediately familiar. I'm probably showing my age here, but it is personally refreshing to be back in the saddle with a design style my group spent many hours refining back as early as 1983 (driven by $20k+ systems, I have to confess) and one I'd like to explore once again later this year.
Lastly, I'd mentioned quite some time ago that at TAI we'd like to apply that design experience to a Signature version of this same model. I've had a very busy year (including, I'm happy to report, a daughter safely and happily off to college this fall and a recent reduction in my CML disease load of 10x, both of which are huge reliefs) but following a personal move to a new studio in about 45 days, I expect to finally follow through on my promise and release a limited instance of this basic model (yes, mods will be retro-fitable). In short, I'll be installing hand-wired electronics behind the D2.1se's cabinet and drivers, including silver, teflon-in-foil, and wound foil, together with my version of the filter geometries I think more deeply explore "organic" sound.
So, many and sincere thanks for the bandwidth to express these somewhat more personal thoughts and inspirations, folks, and I stand by for any and all assistance that we at TAI can provide. We've made many friends over the last few years and we truly enjoy doing what we do. Ultimately, as the man said, it's only audio. To which I'd add, which should be about serving the music!