What's written in the HX schematic diagram at the jacks, and confirming it with calculations of the circuits involved.
Pretty much industry standard, everyday instrument level impedance.
Multimeter would be more of the standard bulk DC resistance. Subtle difference between that and impedance, which
considers reactance of any capacitors or inductors involved. Both are correct, one is a passive reading, the other circuit
active.
Resistance is the resist of a circuit not including reactance in a circuit that is passive. Reactance occurs when a
voltage/signal is applied and reactance becomes parts of it. Impedance by definition, is a function of frequency,
which infers the presence of a voltage/signal. Resistance doesn't require that.
Phil and Ben have the passive aspects, while I managed to dig out the active aspects that are more to do with impedance
as specified in the documents, rather than just resistance. We're all pretty much correct on that one.