Impedance Mismatch: A.I. M3A, Krell KSA100

Yeah, but it depends whether that 1.2K is over the entire audioband. If, say, below 100Hz preamp's output impedance gets higher (I believe Stereophile showed that to be the case for the Aesthetix preamp), then an amp with the input impedance of 22K may not be a good match.
My personal opinion to be taken with a grain of salt is that for an amp with the input impedance of less than 50K the best match in a tube preamp would be one that is transformer coupled. That keeps the output impedance low over the entire audioband and guarantees electrical compatibility.

I have an Audio Horizons preamp matched witha KSA-100S. Match made in heaven.

Romandoc is correct. The value of the output coupling cap in tube preamps can significantly increase the output impedance of a tube preamp in the bass frequencies as compared to the rated output impedance at 1 KHZ. The actual output impedance of the Modulus,is probably significantly higher than 1200 ohms at 20 HZ. I would also suggest that the optimal impedance ratio is better at 20:1 or 30:1.

I have a Modulus 3A preamp coupled with a Stratos Extreme stereo amp with a 22K input impedence. It is a match made in heaven. I am smitten with the sound and couldn't ask for any better. I would suspect your Krell amp with the 22K input impedence would be a great match as well.

Bob

Should be no problem providing you don't run very long, high capacitance interconnect cables. We know of many Krell owners who also own an M3A with excellent results. Regards, AI Technical