The only thing you have to match is the output impedence of the pre-amp with the input impedence of the power amp.
Since he is matching an Ayre preamp with an Ayre amp, I don't think there should be any impedance mismatch.
Another K-5xe MP preamp just posted today, at an even lower price.
https://www.audiogon.com/listings/lis8fb1d-ayre-acoustics-k-5xe-mp-excellent-condition-solid-state
Next thing you know there will be a thread titled "Why so many Ayre K-5xe MP preamps for sale?".