"Remember that caps used in passive crossover see high voltages and therefore they change shape along with the signal flowing through them - this can add significant distortion in some cases"
Both Claritycap MR and Duelund reportedly have design improvements that minimize this physical movement of the capacitor plates(resonance). Clarity has a white paper in which they claim that in extensive listening tests, low capacitor resonance was a greater factor than capacitor material, in determining listeners' perceptions of a capacitor's quality.
Bob, when I rebuilt my Merlin crossovers I found that adding a .015uf russian FT-1 teflon bypass cap in parallel with the stock midrange/woofer main cap made a small improvement in speed & precision of the driver. When the cap is fully broken in, I will remove it and listen carefully for the mid-range bump you describe.
