I'd say the JBL M2. You do need the special-sauce Crown DSP amps (or a BSS processor with the appropriate EQ curves), but with the special waveguide and the DSP it has an almost perfectly flat frequency response throughout its range not only on-axis, but a near-perfect off-axis response as well.
most advanced speaker in a rectangular wooden box?
As you move up the scale of ingenuity and price, speakers take on different, sometimes fantastic, shapes and are made out of different, sometimes exotic, materials. So what would you nominate as the most advanced design that still houses its drivers in an essentially rectangular box made of some kind of wood product?