Again, in normal circumstances you are unlikely to have a problem with or hear a difference between 2 identical tube preamps, one with 1.5k ohms output impedance, and the other with 3k ohms output impedance, using your amp with 30k input impedance, if you're not running long interconnects (unbalanced) and or biamping, even though you've halved the ratio with the 3k ohm preamp.
I had a problem with my system once when biamping 2-22k ohm input impedance SS amps from a preamp with 3k ohms output impedance unbalanced. The biamping also added extra cables. There was definitely a loss of dynamics and drive to the system. When the ratio gets that low, 3-4:1 you're going to hear it. Ultimately, I solved the problem with the Microzotl. Same low output impedance like a SS preamp, but with tubes.