where to go from here..,,

10X rule is the MINIMUM for impedance matching.

Most power amps designed to work well with tube pre-amps in general have input impedance of 60Kohm or higher, to be safe.

That is an insurance policy for good results with most any tube preamp. PRe-amp output impedance can vary widely with frequency and generalized specs may not indicate actual output impedance at particular frequencies.

So my rule of thumb for a good insurance policy is to avoid using a tube pre-amp with power amps with input impedance specs less than 60000Kohm.

That's not to say there will not be cases that might still work well and sound fine, but it can be hard to determine for certain, so better to just play it safe.

In general I would hesitate to use a tube preamp with an amp rated 22kohms input impedance, unless known for certain to have particularly low output impedance at all frequencies for a tube preamp. Less than optimal impedance matching will limit dynamics and add distortion. Might still sound OK, just not optimal.

"In the face of Mapman's rule of thumb, all of our preamps work fine with 10K amplifier inputs no worries."

Fine is fine, but not necessarily best.

"Best" is even a subjective judgement. May or may not be based on anything quantitative.

Just saying. Its all good. Just a matter of how good. Personal preferences mostly determine that in the end.

Atmasphere.

That certainly helps the buyer in the case of your stuff.

The rule I specified is designed as a general insurance policy in cases where it may not be clear based on specs or any other published info. As the amp input impedance goes up, within reason I suppose, the chances of hearing a difference goes down. 60Kohm input impedance spec seems to be a safe lowest common denominator based on teh specs I see published for products explicitly designed to work well with tube pre-amps in general.