For those with balanced connections all round, NHT Pro makes a great little passive attenuator which is balanced I/O, yet also comes with a pair of adaptors. Matches the amp as well.
Channel Islands, Luminous Audio, DaCT, Goldpoint, all make very good quality passive devices. I chose the DaCT, hardwired into the amp, with the Bent Audio remote control retro fit, in my ZR1000.
Even the Nixon DACkit @ 1.6V output has enough juice to work well in this application. The amps have variable input sensitivity.