The general rule of the thumb is, the input impedance of the amp should be ~15 times or more than the output impedance of the pre (or the source unit, generally speaking). That's generalising, of course.
As Aporter mentions, amps with 10k inputs are a tad difficult to match, while others with 150k are very easy to drive.
As Aporter mentions, amps with 10k inputs are a tad difficult to match, while others with 150k are very easy to drive.