With that 15kohm inout impedance I would only go with the Pass B1 Buffer, not quite passive, but awfully close. For some reason the GON consensus seems to be that TVC and AVCs (I've owned both from Bent and K&K, as well as the Placette Active and RVC)are always better than resistor based passive. With my Cardas GR IC (very low capaitance) and Music Reference RM9 Special Edition I find the Gold Point Volume Attenuator SA1 works just as well to my ears. Plenty of soundstage, dynamics, and clarity. The technoids can proabably explain it better, but I get the sense that TVC and AVCs are also problematic, though they do provide a partial solution to impedance mismatches. To my ears, with properly matched source and amps, the resistor-based attenuators are undeniably simpler, purer, and capable of even lower distortion - but they do have to be in the "right" system for them to perform their best.
