Hattor Audio preamps?

I have one that’s got all the upgrades and the tube stage as well. It’s a superb preamp for sure.  In my system, the tube stage adds a lot to the sound being amazing.  I recently compared to the Benchmark and there was no comparison, the Hattor is worlds better.  This piece oozes quality and sounds incredible.

Can someone give me the rundown again as to the rule of impedance compatibility?

Thanks!

the higher the input impedance of the power amplifier, the better, the minimum from which I would probably be interested in passives is 50k

I've used a Khozmo volume control/ "preamp" for several years now in two different iterations, and I would be hard pressed to go back to an active preamp despite having owned a few excellent ones through the years.  Sonically, it's about as transparent as you can get and is the embodiment of simplicity.  Build quality is top notch, and customer service from Arak (despite being in Poland) has been exemplary.  My highest recommendation.

I do not own the Hattor but own Arek's Khozmo passive. Excellent passive but definitely prefer the Dave Slagle autofomers!