I have no knowledge of how true it may be, but according to
this post, "Actually the Shindo pre-amps all have a very low output impedance. The numbers often seen in their specs is the lowest possible input impedance of the partnering amplifier." You should probably check that with the manufacturer or distributor.
If the output impedance is truly 5K, it would be an acceptable match only if two conditions are satisfied:
1)The output impedance is essentially flat with frequency. That is unlikely to be the case if a coupling capacitor is used at the output, which would typically cause the output impedance to rise substantially at deep bass frequencies, resulting in rolloff of those frequencies.
2)The length of the interconnect cable is short, and the cable has low capacitance per unit length. Otherwise the upper treble will be rolled off to some degree. That would occur regardless of power amp input impedance, as it is due to the interaction of high preamp output impedance with cable capacitance.
Regards,
-- Al