10K Ohms is too low for tube preamps? Since when? That’s relatively, but not absolutely, high. Low impedance to me is in the 600 to 5K range.
Please keep in mind that a "low impedance amplifier" is not the same as with low impedance speakers. The amps present a flat, resistive load. This means that there are no hills and valleys in the response curve like with a speaker attached to a tube amp.
Worst case scenario for most tube preamps is that you will lose a little bass due to the output coupling capacitor which is in the 1uF to 4uF range and a little maximum gain (which you don’t use anyway).
A tube pre with 1uF output caps could be down around 5 dB at 20 Hz (I’m in the middle of a few things so my math could be a little off). With 2uF caps around -2.9 dB. This may actually be helpful in the right room!
Look at this example:
https://www.stereophile.com/content/zesto-leto-ultra-ii-line-preamplifier-measurements
It handles 600 Ohms output just fine. My point is, we can't universally exclude 10K input impedance amp from use with tube pres. Some may do awful with it, but I suspect many will be fine.
Please keep in mind that a "low impedance amplifier" is not the same as with low impedance speakers. The amps present a flat, resistive load. This means that there are no hills and valleys in the response curve like with a speaker attached to a tube amp.
Worst case scenario for most tube preamps is that you will lose a little bass due to the output coupling capacitor which is in the 1uF to 4uF range and a little maximum gain (which you don’t use anyway).
A tube pre with 1uF output caps could be down around 5 dB at 20 Hz (I’m in the middle of a few things so my math could be a little off). With 2uF caps around -2.9 dB. This may actually be helpful in the right room!
Look at this example:
https://www.stereophile.com/content/zesto-leto-ultra-ii-line-preamplifier-measurements
It handles 600 Ohms output just fine. My point is, we can't universally exclude 10K input impedance amp from use with tube pres. Some may do awful with it, but I suspect many will be fine.