Not all preamps that have equal output impedance specs, say 600 ohms, have the same impedance across the frequency band, and often much higher at the lower (bass) frequencies. The result would be a loss of mid/low bass with those having this condition when paired with an amp having low input impedance.
To mate a preamp with a 10K input impedance amp one would need to know the output impedance of the preamp across the frequency range.
To mate a preamp with a 10K input impedance amp one would need to know the output impedance of the preamp across the frequency range.