Newer Quads have a lower impedance than the older ones, as Quad contiues down the same path that Martin-Logan took, trying to get transistors to work with ESLs. But the nature of ESLs is that tubes will drive them without high end empahsis and better bass impact. So to deal with the low impedance, you may need a set of ZEROs to get a tube amp to work, but then it will be easy.
