I would try to follow the "eight to one" rule and mate it with an amp with a VERY low input impedance. But, I don't know of any amps with a 4k to 5k input impedance.
Nonetheless, a low input impedance will allow your preamp to be "a good performer during high-power demands" like Aball says.
YBAs are, usually, 27k. You could even biamp with those! And feed them well. (Because you'd, still, be sending your signal into 13.5k).
Maybe, there's a complementary German amp you should explore. . .