Aronov SA60/960 power amps input impedance?

Hi ,I have and ARONOV SA60 Power amp which is the older model of the 960, but exactly the same except cosmetically. I am trying to integrate a Vandersteen sub and need to know the imput impedance. The manual does not say and the Aronovs have packed up shop and are no where to be found. Can anyone help out . Thanks in Advance , Jed